"Listed below are the fifty most significant science fiction / fantasy novels, 1953—2002, according to the Science Fiction Book Club: bold the ones you have read, italicize the ones you started but never finished, underline the ones you own but never started, strike out the ones you hated, and put an asterisk beside the ones you love. "

+1. The Lord of the Rings, J.R.R. Tolkien*
+2. The Foundation Trilogy, Isaac Asimov*
+3. Dune, Frank Herbert
+4. Stranger in a Strange Land, Robert A. Heinlein*
5. A Wizard of Earthsea, Ursula K. Le Guin
+6. Neuromancer, William Gibson
+7. Childhood's End, Arthur C. Clarke
+8. Do Androids Dream of Electric Sheep?, Philip K. Dick
9. The Mists of Avalon, Marion Zimmer Bradley
+10. Fahrenheit 451, Ray Bradbury*
11. The Book of the New Sun, Gene Wolfe
+12. A Canticle for Leibowitz, Walter M. Miller, Jr.
+13. The Caves of Steel, Isaac Asimov*
14. Children of the Atom, Wilmar Shiras
15. Cities in Flight, James Blish
16. The Colour of Magic, Terry Pratchett
+17. Dangerous Visions, edited by Harlan Ellison
+18. Deathbird Stories, Harlan Ellison*
19. The Demolished Man, Alfred Bester
20. Dhalgren, Samuel R. Delany
21. Dragonflight, Anne McCaffrey
+22. Ender's Game, Orson Scott Card*
+23. The Chronicles of Thomas Covenant by Stephen R. Donaldson
24. The Forever War, Joe Haldeman
+25. Gateway, Frederik Pohl
+26. Harry Potter and the Philosopher's Stone, J.K. Rowling*
+27. The Hitchhiker's Guide to the Galaxy, Douglas Adams
28. I Am Legend, Richard Matheson
+29. Interview with the Vampire, Anne Rice
+30. The Left Hand of Darkness, Ursula K. Le Guin
31. Little, Big, John Crowley
32. Lord of Light, Roger Zelazny
33. The Man in the High Castle, Philip K. Dick
34. Mission of Gravity, Hal Clement
35. More Than Human, Theodore Sturgeon
36. The Rediscovery of Man, Cordwainer Smith
+37. On the Beach, Nevil Shute
+38. Rendezvous with Rama, Arthur C. Clarke
+39. Ringworld, Larry Niven
40. Rogue Moon, Algis Budrys
41. The Silmarillion, J.R.R. Tolkien
+42. Slaughterhouse-5, Kurt Vonnegut*
+43. Snow Crash, Neal Stephenson*
44. Stand on Zanzibar, John Brunner
+45. The Stars My Destination, Alfred Bester*
+46. Starship Troopers, Robert A. Heinlein
47. Stormbringer, Michael Moorcock
+48. The Sword of Shannara, Terry Brooks
49. Timescape, Gregory Benford
50. To Your Scattered Bodies Go, Philip Jose Farmer

Since I couldn't figure out how to make things show up underlined or bolded or italicized, I just put +'s in front of those I read, and *'s in back of those I loved. I have a couple of them on the shelf, unread, notably THE MISTS OF AVALON and THE MAN IN THE HIGH CASTLE. And I didn't HATE any of the ones I read.

The list, as noted, is apparently from the Science Fiction Book Club, and these are the SF novels they consider to be the most influential. It's a pretty good list, I think.

I stole it from someone's SF blog.