Here is a link to the Phobos Entertainment's Top 100 SF Books.  And here is are the ones I have read (with revenue making links to Amazon added).

2.   Foundation Written by Isaac Asimov
7.   Frankenstein Written by Mary Wollstonecraft Shelley
16.   Ringworld Written by Larry Niven
28.   20,000 Leagues Under the Sea Written by Jules Verne (never finished)
33.   Neuromancer Written by William Gibson
34.   Ender’s Game Written by Orson Scott Card
46.   I, Robot Written by Isaac Asimov
49.   Brave New World Written by Aldous Huxley
53.   Snow Crash Written by Neal Stephenson
57.   Startide Rising Written by David Brin
63.   Flowers for Algernon Written by Daniel Keyes
65.   The Postman Written by David Brin
68.   Flatland Written by Edwin Abbot
69.   the Planiverse Written by A.K. Dewdney
82.   Red Mars Written by Kim Stanley Robinson
85.   The Hitchhiker’s Guide to the Galaxy Written by Douglas Adams
95.   Mars Written by Ben Bova

Only 17 out of 100.  How sad. 

I was very happy, although not surprised, to see Startide Rising and The Postman on the list.  Those are two of my favorite books both by David Brin (please don't judge him by  that awful Kevin Costner movie).  If you want to read another really great David Brin book check out The Kiln People.