David Langford's Top 20 Pre-1990 Genre Novels

I discovered (or rediscovered) this list a while back. It was compiled by multi-Hugo-winning SF&F critic David Langford back in 2002 for an SFX special. Working on the basis that it takes a decade for a book to proves its classic status, he decided to only go up to works published in 1989 to compile the list.

The Top Twenty
20. Guards! Guards! by Terry Pratchett
19. Gateway by Frederick Pohl
18. Consider Phlebas by Iain M. Banks
17. Cyteen by C.J. Cherryh
16. Bridge of Birds by Barry Hughart
15. The Affirmation by Christopher Priest
14. Lord of Light by Roger Zelazny
13. The Three Stigmata of Palmer Eldritch by Philip K. Dick
12. The Owl Service by Alan Garner
11. The Stars My Destination by Alfred Bester
10. Rogue Moon by Algis Budrys
09. Blood Music by Greg Bear
08. Dune by Frank Herbert
07. Gormenghast by Mervyn Peake
06. Earthsea by Ursula K. LeGuin
05. Pavane by Keith Roberts
04. The Lord of the Rings by J.R.R. Tolkien
03. The City and the Stars by Arthur C. Clarke
02. Little, Big by John Crowley
01. The Book of the New Sun by Gene Wolfe

Bubbling Under
Helliconia Spring by Brian W. Aldiss
The Shockwave Rider by John Brunner
The Infernal Desire Machines of Dr. Hoffman by Angela Carter
The Man Who Was Thursday by G.K. Chesterton
The Dark is Rising by Susan Cooper
Babel-17 by Samuel R. Delaney
Mythago Wood by Robert Holdstock
Fire and Hemlock by Diana Wynne Jones
The Lathe of Heaven by Ursula K. LeGuin
A Wreath of Stars by Bob Shaw

Short Story Collections
The Wallet of Kai Lung by Ernet Bramah
The Martian Chronicles by Ray Bradbury
The Exploits of Engelbrecht by Maurice Richardson
The Dying Earth by Jack Vance
The Terminal Beach by J.G. Ballard
Cosmicomics by Italo Calvino
Neutron Star by Larry Niven
Nine Hundred Grandmothers by R.A. Lafferty
Deathbird Stories by Harlan Ellison
The Rediscovery of Man by Cordwainer Smith

Ten of the Worst
Ralph 124C41+ by Hugo Gernsback
They'd Rather Be Right by Mark Clifton and Frank Riley
March of the Robots by Rev. Lionel Fanthorpe (writing as Leo Brett)
The Number of the Beast by Robert Heinlein
Battlefield Earth by L. Ron Hubbard
O-Zone by Paul Theorux
The Troglodytes by Nal Rafcam
The Eye of Argon by Jim Theis
The Black Star by Lin Carter
Flight by Vanna Bonta

The original link also contains rationales for the choices, explanations for some notable missing books (Langford considers the original Hyperion Cantos to be one long novel, so he seems to have ruled Hyperion ineligible despite just scraping in before the date), some other books he rates between 1990 and 2002 and so on.

I quite like the lists. Giving a work some time before proclaiming it 'the greatest thing ever' makes sense.

For an alternative list, check out Stego's list of his top 100 books here.