I think this thread could do with some more entries, so here are some of my favourites:
29. "Cities in Flight" series (originally 4 books, probably published as 1 now) - James Blish
30. Engine Summer - John Crowley (most often available as part of a collection called "Three Novels" or "Otherwise")
31. The Worm Ouroboros - E. R. Eddison
32. Diaspora - Greg Egan
33. Ash: A Secret History - Mary Gentle
34. "A Sarantine Mosaic" series (2 books) - Guy Gavriel Kay (this got me hooked on Byzantine history)
35. The Left Hand of Darkness - Ursula K. le Guin
36. Good Omens - Terry Pratchett & Neil Gaiman
37. Norstrilia - Cordwainer Smith (his short stories are also very good)
38. A Fire Upon The Deep - Vernor Vinge