yeah another list/poll, this one from Locus in the SF/F categories:
http://www.locusmag.com/2012/AllCent...lsResults.html
20th Century SF Novel:
Rank Author : Title (Year) Points Votes
1 Herbert, Frank : Dune (1965) 3930 256
2 Card, Orson Scott : Ender's Game (1985) 2235 154
3 Asimov, Isaac : The Foundation Trilogy (1953) 2054 143
4 Simmons, Dan : Hyperion (1989) 1836 131
5 Le Guin, Ursula K. : The Left Hand of Darkness (1969) 1750 120
6 Adams, Douglas : The Hitchhiker's Guide to the Galaxy (1979) 1631 113
7 Orwell, George : Nineteen Eighty-Four (1949) 1493 105
8 Gibson, William : Neuromancer (1984) 1384 100
9 Bester, Alfred : The Stars My Destination (1957) 1311 91
10 Bradbury, Ray : Fahrenheit 451 (1953) 1275 91
Rest of list and others (fantasy, 21st century) at:
http://www.locusmag.com/2012/AllCent...lsResults.html