n.b. not all of his stories make use of his Cthulhu mythos, and nor are those that do completely consistent with one another. the mythos developed slowly, as he wrote, and was not systematised in his lifetime.
to enquire further & to Order: e-mail me; v$imt$v at my subdomain, i-m-t.demon.co.uk (written out to reduce harvesting by spamlist-builders)

• The H. P. Lovecraft Omnibus volume 1: At the Mountains of Madness new copy, Voyager (HarperCollins) reprint. cover Tim White. ukL 3.95
  slight creasing in spine, else fair secondhand copy
• The H. P. Lovecraft Omnibus volume 1: At the Mountains of Madness new copy, Voyager (HarperCollins) 2nd print. cvr Tim White. ukL 7.99 (out of stock)
  Essay: H.P.Lovecraft's Novels by August Derleth; At the Mountains of Madness; The Case of Charles Dexter Ward; The Dreams in the Witch-House; The Statement of Randolph Carter; The Dream-Quest of Unknown Kadath; The Silver Key; Through the Gates of the Silver Key.
  previous incarnations of this edition: Grafton/Granada 1985 with eight printings; HarperCollins 1993 with another eight printings; first uk publication by Victor Gollancz 1966
• The H. P. Lovecraft Omnibus volume 2: Dagon and other Macabre Tales new copy, HarperCollins 1994 reprint. cover Tim White ukL 3.95
  slight creasing in spine, else fair secondhand copy
• The H. P. Lovecraft Omnibus volume 2: Dagon and other Macabre Tales new copy, HarperCollins reprint. cover Tim White ukL 7.99 (out of stock)
  Lovecraft's major essay, "Supernatural Horror in Literature" is also included (written 1926-7, largely revised 1933-5)
• The H. P. Lovecraft Omnibus volume 3: The Haunter of the Dark and other tales new copy, HarperCollins reprint. cover Tim White. ukL 3.95
  slight creasing in spine, else fair secondhand copy
• The H. P. Lovecraft Omnibus volume 3: The Haunter of the Dark and other tales new copy, HarperCollins reprint. cover Tim White ukL 7.99 (out of stock)
  intro. August Derleth; The Outsider; The Rats in the Walls; Pickman's Model; The Call of Cthulhu; The Dunwich Horror; The Whisperer in Darkness; The Colour Out of Space; The Haunter of the Dark; The Thing on the Doorstep; The Music of Erich Zann; The Lurking Fear; The Picture in the House; The Shadow over Innsmouth; The Shadow out of Time.
  (this omnibus adds the four last-listed stories to the contents of the 1951 Victor Gollancz edition of The Haunter of the Dark, which was paperbacked by Panther & saw four reprintings.)
• The Haunter of the Dark and other tales Panther (Granada) 2nd print. 1972 (after 2 pre-Granada prints.) secondhand copy, poor to fair (front hinge creased one third open after title p, spine lightly rolled, pages yellowed & beginning to brown) ukL 2.95
  intro. August Derleth; The Outsider; The Rats in the Walls; Pickman's Model; The Call of Cthulhu; The Dunwich Horror; The Whisperer in Darkness; The Colour Out of Space; The Haunter of the Dark; The Thing on the Doorstep; The Music of Erich Zann
• The Tomb and other stories Panther (Granada) 3rd print. secondhand copy, fair to good (front hinge creased open, two inch crease in front cover from base to half an inch up from base at edge; first 58pp decreasingly [sorry] creased to match) ukL 4.99
  title story; The Festival; Imprisoned with the Pharaohs; He; The Horror at Red Hook; The Strange High House in the Mist; In the Walls of Eryx; The Evil Clergyman; Early Tales: The Beast in the Cave; The Alchemist; Poetry and the Gods; The Street; The Transition of Juan Romero; Fragments: Azathoth; The Descendants; The Book; plus a Complete Chronology of his work by Lovecraft.

• Brian Lumley's Mythos Omnibus. new copy, HarperCollins 1997 First printing cvr unattrib. ukL 6.99
  contains The Burrowers Beneath, The Transition of Titus Crow, & The Clock of Dreams.
• Brian Lumley's Mythos Omnibus Volume Two new copy, HarperCollins 2nd printing cvr unattrib. ukL 6.99
  contains Spawn of the Winds, In the Moons of Borea & Elysia
• In the moons of Borea new copy, Grafton ukL 4.99
  n.b. missing title page, pages beginning to yellow; cvr George Underwood
• The Clock of Dreams new copy, Grafton 2nd printing ukL 4.99
  cvr George Underwood. pages beginning to yellow
• The Compleat Crow new copy, N.E.L. 1997 ukL 6.99 (out of stock)
  cvr George Underwood. collects all of the Titus Crow novelettes & short stories
• The Compleat Crow new copy, received damaged N.E.L. 1997 First printing ukL 3.95
  cvr George Underwood; front+back covers & front fly creased, base of spine scraped, effectively poor-fair s/h copy
  collects all of the Titus Crow novelettes & short stories
• Fruiting Bodies and Other Fungi Roc/Penguin (out of stock)
• Return of the Deep Ones and other Mythos Tales new copy, Roc/Penguin 2nd print. ukL 6.99 (in stock, out of print)
  Inception (short Titus Crow story); Lord of the Worms (novella); Beneath the Moors (novel); The Return of the Deep Ones (novel)
• Psychomech secondhand copy, Grafton ukL 2.95 (out of print)
  missing title page; spine sun-faded & pages beginning to yellow, spine slightly creased (but not broken) from about halfway up, towards top
• Psychamok secondhand copy, Grafton 3rd printing ukL 3.95 (out of print)
  cvr George Underwood; spine "lightly creased" (but not broken) down one line, front cover slightly worn, pagesjust beginning to yellow, else good copy (middle book of the trilogy is Psychosphere)
• The Second Wish and Other Exhalations N.E.L. First Edition 1995 ukL 8.99 (this edition out of print)
  cvr Les Edwards; new copy; contents includes Cthulhu mythos & other stories: intro. by Lumley; The Second Wish; The Sun, the Sea and the Silent Scream; Dr. Marigny's Clock; The Luststone; Mother Love; What Dark God?; The Thief Immortal; The House of the Temple; Back Row; Name and Number; Snarker's Son; Rising with Surtsey; David's Worm.
• Ship of Dreams Headline 1989 First uk edition ukL 4.99 (out of print)
  cvr Marl Salowski; new copy, pages beginning to yellow
• Sorcery in Shad: Tales of the Primal Land vol.3 Headline 2nd printing ukL 4.99 (out of print)
  cvr Melvyn; new copy, pages beginning to yellow

• Necroscope new copy, Voyager (HarperCollins) 7th print. cvr George Underwood. ukL 6.99
• Necroscope II: Wamphyr! new copy, HarperCollins 5th print. cvr George Underwood. ukL 6.99 (out of stock)
• Necroscope III: The Source new copy, HarperCollins 7th print. cvr George Underwood. ukL 6.99 (out of stock)
• Necroscope IV: Deadspeak new copy, HarperCollins 5th print. cvr George Underwood. ukL 5.99
• Necroscope V: Deadspawn new copy, HarperCollins 2nd print. cvr George Underwood. ukL 5.99
• E-Branch: Invaders new copy, N.E.L. 5th print. cvr George Underwood. a.k.a. Necroscope: Invaders ukL 6.99
• Necroscope: Defilers new copy, N.E.L. First p/b print. cvr Bob Eggleton. sequel to the above. ukL 6.99 (out of stock)
• Vampire World 1: Blood Brothers new copy, ROC (uk) 12th print. cvr George Underwood. ukL 7.99
• Vampire World 2: The Last Aerie new copy, ROC (uk) 7th print. cvr George Underwood. ukL 8.99
• Vampire World 3: Bloodwars new copy, ROC (uk) 7th print. cvr George Underwood. ukL 7.99
• Necroscope: The Lost Years volume 1 new copy, N.E.L. 8th print. cvr unattrib. but looks to be by George Underwood. ukL 6.99
• Necroscope: The Lost Years volume 2 new copy, N.E.L. First print. cvr George Underwood. ukL 6.99 (out of stock)

the above are "a format" uk paperbacks - very slightly taller and deeper than the more-or-less standard merkin mass-market paperback format.

• The Antarktos Cycle: At the Mountains of Madness and Other Chilling Tales ed. Robert M. Price. new copy, Chaosium 8/99 First Edition (out of stock, & out of print; last one was ukL 17.99)
• The Azathoth Cycle: The Blind Idiot God ed. Robert M. Price. new copy, Chaosium 3/95 First Edition ukL 14.99 (in stock, though out of print)
• The Book of Eibon - New in January 2002 new copy, Chaosium 2nd print; on 100% acid-free paper ukL 14.99
  Histories of the Elder Magi, Episodes of Eibon of Mhu Thulan, the Papyrus of the Dark Wisdom, Psalms of the Silent, and the Eibonic Rituals: by Lin Carter, Michael Cisco, Laurence J. Cornford, Micheal Fantina, John R. Fultz, Robert M. Price (also editor of the book), Joseph S. Pulver, Ann K. Schwader, Stephen Sennitt, Clark Ashton Smith, Richard L. Tierney
• The Book of Iod: The Eater of Souls & other tales by Henry Kuttner (one by Kuttner + Robert M. Bloch, plus one each by Lin Carter and Robert M. Price) Chaosium 5/95 First Edition (out of stock & out of print)
• The Complete Pegana: All the Tales Pertaining to the Fabulous Realm of Pegana by Lord Dunsany. new copy, Chaosium February 1998 First Edition. (last copy was ukL 14.99; out of stock & out of print)
• The Cthulhu Cycle: Thirteen Tentacles of Terror ed. Robert M. Price. Chaosium July 1996 First Edition. (out of stock)
• Cthulhu's Heirs ed. Thomas M. K. Stratman. new copy, Chaosium 2nd print. ukL 14.99 (in stock, though out of print)
• Delta Green: Dark Theaters ed. Bob Kruger & John Tynes; Armitage House November 2001 First Edition ukL 12.99
  intro: A Word of Explanation - Tynes; Once More, From The Top - A. Scott Glancy; Night and Water - Dennis Detweiler; Russian Dolls - Robert E. Furey; As I See It - Greg Stolze; Suicide Watch - Arinn Dembo; The Corn King - Tynes; Good Night, Bach Ma, Good-Bye - Benjamin Adams; The Fast Track - Martin E. Cirulis.
• Delta Green: Denied to the Enemy by Dennis Detweiler; Armitage House March 2004 First Edition ukL 12.99
  A Cthulhu Mythos novel of World War II
• Delta Green: The Rules of Engagement by John Tynes; Armitage House February 2000 First Edition ukL 11.99
  A Cthulhu Mythos novel of Personal Apocalypse
• The Disciples of Cthulhu ed. Edward P. Berglund. new copy, Chaosium 2nd revised edition, February 1996 First printing = First Thus; ukL 14.99 (in stock, though out of print)
• The Disciples of Cthulhu II ed. Edward P. Berglund - new in 23rd May 2003 Chaosium February 2003 First Edition ukL 10.99
  The Bookseller's Second Wife - Walter C. DeBrill jr, Eldritch - Brad Linaweaver & Fred Olen Ray, The Web - Gary Myers, Passing Through - Robert Weinberg, The Idol - Scott David Aniolowski, Time in the Hourless House - A. A. Attanasio, Special Order - Henry Lee Forrest, Lujan's Trunk - Donald R. Burleson, The San Francisco Treat - C. J. Henderson, Acute Spiritual Fear - Robert M. Price, The Eldridge Collection - Will Murray, An Arkham Home Companion - Brad Strickland, The Last Temptation of Ricky Perez - Benjamin Adams
• The Dunwich Cycle: Where the Old Gods Wait ed. Robert M. Price. new copy, Chaosium November 1995 First Edition (last copy was ukL 14.99; out of stock & out of print)
• Frontier Cthulhu - NEW ORIGINAL ANTHOLOGY - in 3rd January 2008 ukL 7.99
  15 New Tales of the Cthulhu Mythos by authors familiar & unfamiliar
• The Hastur Cycle ed. Robert M. Price. new copy, Chaosium October 1993 First Edition. ukL 14.99 (in stock, though out of print)
• The Ithaqua Cycle: The Wind-Walker of the Icy Wastes ed. Robert M. Price. Chaosium July 1998 First Edition. ukL 14.99 (in stock, though out of print)
• Made in Goatswood: New Tales of Horror in the Severn Valley ed. Scott David Aniolowski. Chaosium July 1995 First Edition ukL 14.99 (in stock, though out of print)
  Original anthology of mythos stories, including one by him, set in Campbell's Goatswood milieu; the associated major Call of Cthulhu Source & Campaign Book is Ramsey Campbell's Goatswood and Less Pleasant Places
• The Mask of Cthulhu: Horrific Tales of the Cthulhu Mythos by August Derleth. new copy, Carroll & Graf mass-market paperback 1996 1st printing (out of stock & out of print; was ukL 4.99)
  includes the Derleth-completed Lovecraft story, "The Return of Hastur"; "The Whippoorwill in the Hills", "Something in Wood"; "The Sandwin Compact"; "The House in the Valley"; "The Seal of R'lyeh".
• Mysteries of the Worm by Robert M. Bloch. new copy, Chaosium October 1993 2nd. (enlarged) edition, First printing = First Thus; ukL 14.99 (in stock, though out of print)
• Nameless Cults: The Cthulhu Mythos Fiction of Robert E. Howard Chaosium December 2001 First Edition stated printed on 100% acid-free paper. ukL 14.99 (in stock though out of print)
• The Necronomicon: Selected Stories and Essays concerning the Blasphemous Tome of the Mad Arab ed. Robert M. Price. new copy, Chaosium revised edition, 1st printing = First Thus; ukL 14.99
• Nightmare's Discyple novel by Joseph S. Pulver, sr; interior b+w art (title & contents pp. border & chapter heads) by Thomas Brown & Dave Carson; new copy but bottom fly corner of front cover, fly + title pp. stained; Chaosium 1999 First Edition stated printed on 100% acid-free paper. (out of print; was ukL 14.99) ukL 12.99
• The Nyarlethotep Cycle ed. Robert M. Price, interior b+w art (title & contents pp. border & chapter heads) by Dave Carson; new copy, Chaosium May 1997 First Edition (out of stock & out of print; last copy was ukL 14.99)
• The Opener of the Way by Robert Bloch (new, a one eighth of an inch mechanical dent in the rear cover, else vg+ copy Panther 1976 First uk p/b, cvr anthony roberts) ukL 7.99
• The Opener of the Way by Robert Bloch (secondhand copy, poor to fair only condition, market stall stamp & biro'd price on inside front cover. Panther 1976 First uk p/b, cvr anthony roberts) ukL 0.95
• Return to Lovecraft Country ed. Scott David Aniolowski; new copy, Triad 1997 First Edition. ukL 9.99 (out of stock)
• Scroll of Thoth: Simon Magus and the great Old Ones by Richard L. Tierney. new copy, Chaosium September 1997 First Edition. (out of stock)
• Shards of Darkness by E. P. Bergland. new copy, Mythos 2000 First Edition. ukL 9.99
• Shub-Niggurath Cycle ed. Robert M. Price. new copy, Chaosium 2nd print. (out of stock, out of print)
• Singers of Strange Songs ed. Scott David Aniolowski. Chaosium August 1997 First Edition. ukL 10.99
• Song of Cthulhu: Tales of the Spheres Beyond Sound ed. Stephen Mark Rainey. new copy, Chaosium August 2001 First Edition. (out of stock)
• The Spiraling Worm: Man versus the Cthulhu Mythos - NEW TITLE - in 1st August 2007 David Conyers & John Sunseri. new copy, Chaosium 2007 First Edition ukL 8.99
  [or "Spiralling Worm" - pp; seven mostly modern day-set tales of the mythos, if i'm not mistaken] intro by C. J. Henderson
• The Strange Cases of Rudolph Pearson - NEW TITLE - in 7th May 2008 First Edition ukL 7.99
  the weird, Cthulhu mythos and cosmic horror investigations of Rudolph Pearson
• Tales out of Innsmouth: New Stories of the Children of Dagon ed. Robert M. Price. new copy, Chaosium September 1999 First Edition stated printed on 100% acid-free paper. ukL 14.99 (in stock, though out of print)
• The Trail of Cthulhu: Horrific Tales of the Cthulhu Mythos by August Derleth. new copy, Carroll & Graf mass-market paperback 1996 1st printing (out of stock & out of print; was ukL 4.99)
• The Tsathoggua Cycle ed. Robert M. Price NEW Title - Chaosium (September) 2005 First Edition. stated printed on 100% acid-free paper. ukL 9.99
  Bat/Trachian (intro) Robert M. Price; From the Parchments of Pnom; The Seven Geases; The Testament of Athammaus; The Tale of Satampra Zeiros; The Theft of the Thirty-Nine Girdles - (all) Clark Ashton Smith; Shadow of the Sleeping God - James Ambuehl; The Curse of the Toad - Loay Hall & Terry Dale; Dark Swwamp - James Anderson; The Old One - John Glasby; The Oracle of Sadoqua - Ron Hilger; The Horror Show - Gary Myers; The Tale of Toad Loop - Stanley C. Sargent; The Crawling Kingdom - Rod Heather; The Resurrection of Kzadool-Ra - Henry J. Vester III
• Where the Deep Ones Are - NEW PARODY - available 13th August 2008 hardcover ukL 10.99
  "The Deep Ones croaked their terrible croaks and smacked their terrible lips and rolled their terrible eyes and waved their terrible flippers..." - retelling by Ken Hite of H. P. Lovecraft's "The Shadow over Innsmouth" as parody classic kids lit.
• The Xothic Legend Cycle: The Complete Mythos Fiction of Lin Carter new copy, Chaosium February 1997 First Edition ukL 12.99 (in stock, though out of print)

• Baby's First Mythos - NEW ITEM Revised 2nd Edition; First Thus & First Hardcover Edition; in 13th January 2005 ukL 6.99
  "From the twisted minds of C.J. Henderson & Erica Henderson Comes the funniest Lovecraft book ever!" An Illustrated Cthuloid abcdary [the "correct" term for "alphabets", or so i am told], and Not Really A Sourcebook At All - except for the pictures, the pictures...
  and now in tasty (well, chewy) board-covered edition, with added X!
• A Cthulhu Mythos Bibliography and Concordance - First Edition March 1999 ukL 16.99
A 463pp (+ preface, etc.) opus by Chris Jaroch-Ernst. awesome.
• The Encyclopedia Cthulhiana by Daniel Harms Chaosium May 1998 revised & enlarged 2nd edition, First printing = First Thus; stated printed on 100% acid-free paper. ukL 11.99

(see also: The Necronomicon, above)