Here is a list I discovered of books published in the Gollancz Fantasy Masterworks line. It does have some overlaps with the lists already posted in this thread. I've underlined everything I have read (some of which I have undoubtedly already noted in previous posts but I can't be bothered to go back and look) though not necessarily in the original editions named below or in the Gollancz reprints but in some edition, and not counting things I started to read but did not finish. I suspect others here can pretty much fill in the rest of the list, since there is little or nothing here that is particularly obscure.
- Poul Anderson, The Broken Sword (Abelard-Schuman, 1954)
- Poul Anderson, Three Hearts and Three Lions (Doubleday, 1961)
- Leigh Brackett, Sea Kings of Mars and Otherworldly Stories (Gollancz, 2005)
- Ray Bradbury, Something Wicked This Way Comes (Simon & Schuster, 1962)
- Jonathan Carroll, The Land of Laughs (Viking, 1980)
- Jonathan Carroll, Voice of Our Shadow (Viking, 1983)
- John Crowley, Aegypt (Bantam Spectra, 1987)
- John Crowley, Little, Big (Bantam, 1981)
- Avram Davidson, The Phoenix and the Mirror (Doubleday, 1969)
- L. Sprague de Camp & Fletcher Pratt, The Compleat Enchanter: The Magical Misadventures of Harold Shea (Nelson Doubleday/SFBC, 1975)
- Lord Dunsany, The King of Elfland's Daughter (Putnam, 1924)
- Lord Dunsany, Time and the Gods (Heinemann, 1906)
- E. R. Eddison, Mistress of Mistresses (Faber and Faber, 1935)
- E. R. Eddison, The Worm Ouroboros (Jonathan Cape, 1922)
- Charles G. Finney, The Circus of Dr. Lao (Viking, 1935)
- Jack Finney, Time and Again (Simon & Schuster, 1970)
- John M. Ford, The Dragon Waiting (Timescape, 1983)
- John Gardner, Grendel (Knopf , 1971)
- Randall Garrett, Lord Darcy (Nelson Doubleday/SFBC, 1983)
- Ken Grimwood, Replay (Arbor House, 1987)
- M. John Harrison, Viriconium (Millennium, 2000)
- William Hope Hodgson, The House on the Borderland and Other Novels (Gollancz, 2002)
- Robert Holdstock, Lavondyss (Gollancz, 1988)
- Robert Holdstock, Mythago Wood (Gollancz, 1984)
- Robert E. Howard, The Conan Chronicles: Volume 1: The People of the Black Circle (Orion/Millennium, 2000)
- Robert E. Howard, The Conan Chronicles: Volume 2: The Hour of the Dragon (Orion/Gollancz, 2001)
- John James, Votan and Other Novels (Orion/Gollancz, 2014)
- Rudyard Kipling, The Mark of the Beast and Other Fantastical Tales (Orion/Gollancz, 2007)
- Ellen Kushner, Thomas the Rhymer (Morrow, 1990)
- Fritz Leiber, The First Book of Lankhmar (Gollancz, 2001)
- Fritz Leiber, The Second Book of Lankhmar (Gollancz, 2001)
- David Lindsay, A Voyage to Arcturus (Methuen , 1920)
- George R. R. Martin, Fevre Dream (Poseidon Press, 1982)
- Patricia A. McKillip, The Forgotten Beasts of Eld (Atheneum, 1974)
- Patricia A. McKillip, Ombria in Shadow (Ace, 2002)
- Patricia A. McKillip, The Riddle-Master's Game (Gollancz, 2001)
- Hope Mirrlees, Lud-in-the-Mist (Collins, 1926)
- Michael Moorcock, Corum: The Prince in the Scarlet Robe (Gollancz, 2002)
- Michael Moorcock, Elric (Gollancz, 2001)
- Michael Moorcock, Gloriana, or The Unfulfill'd Queen (Allison & Busby, 1978)
- Michael Moorcock, The History of the Runestaff (Hart-Davis, MacGibbon, 1979)
- C. L. Moore, Black Gods and Scarlet Dreams (Donald M. Grant, 2002)
- Pat Murphy, The Falling Woman (Tor, 1986)
- Tim Powers, The Anubis Gates (Ace, 1983)
- Tim Powers, The Drawing of the Dark (Ballantine, 1979)
- Tim Powers, Earthquake Weather (Legend, 1997)
- Tim Powers, Expiration Date (HarperCollins UK, 1995)
- Tim Powers, Last Call (Morrow, 1992)
- Fletcher Pratt, The Well of the Unicorn (Sloane , 1948)
- Michael Scott Rohan, The Anvil of Ice (Macdonald, 1986)
- Geoff Ryman, "Was…" (HarperCollins, 1992)
- Lucius Shepard, The Dragon Griaule (Subterranean, 2012)
- Dan Simmons, Song of Kali (Bluejay, 1985)
- Clark Ashton Smith, The Emperor of Dreams: Best Fantasy Tales (Gollancz, 2002)
- Michael Swanwick, The Iron Dragon's Daughter (Millennium, 1993)
- Sheri S. Tepper, Beauty (Doubleday Foundation, 1991)
- Jack Vance, Lyonesse (series, 1989)
- Jack Vance, Lyonesse II: The Green Pearl and Madouc (Orion/Gollancz, 2003)
- Jack Vance, Tales of the Dying Earth (Orion/Millennium, 2000)
- Evangeline Walton, The Mabinogion (Gollancz, 2003)
- Jack Williamson, Darker Than You Think (Fantasy Press, 1948)
- Gene Wolfe, The Citadel of the Autarch (Timescape, 1983)
- Gene Wolfe, The Claw of the Conciliator (Simon & Schuster/Timescape, 1981)
- Gene Wolfe, Peace (Harper & Row, 1975)
- Gene Wolfe, The Shadow of the Torturer (Simon & Schuster, 1980)
- Gene Wolfe, The Sword of the Lictor (Timescape, 1982)
- Jerry Yulsman, Elleander Morning (St. Martin's, 1984)
- Roger Zelazny, The Chronicles of Amber (Orion, 2000)