The List of the 100 SF books you MUST have read. Those I've read are bold. Those I recommend are italicized. (Kinda following on Don's original). Those marked by an asterisk were actually better in their novella forms.
I have a number of divergences with Don. I found Neuromancer tedious, pretentious, and very nearly incomprehensible. I far preferred The Difference Engine and almost anything by Bruce Sterling. J.G. Ballard is definitely an acquired taste, but I have enjoyed nearly every work I've read, short stories to Empire of the Sun
I would concur with these two additions:
Mary Doria Russell, The Sparrow
Gene Wolfe, The Island of Dr. Death and Other Stories and Other Stories
and would further add (although some titles are only arguably SF at all):
Neal Stephenson, The Diamond Age
Niel Gaiman, Coraline
Philip K. Dick, Flow My Tears, the Policeman Said
Fritz Leiber, The Big Time
J.R. Dunn, Days of Cain
Jane Yolen The Devil's Arithmatic
Jane Yolen Briar Rose
Zanna Henderson's "The People" Stories
Cordwainer Smith, The Complete Works--every word beginning to end
And almost anything by Jack Vance
1 Childhood's End, Arthur C. Clarke
2 Foundation, Isaac Asimov
3 Dune, Frank Herbert
4 The Man in the High Castle, Philip K. Dick
5 Starship Troopers, Robert A. Heinlein
6 Valis, Philip K. Dick
7 Frankenstein, Mary Wollstonecraft Shelley
8 Gateway, Frederik Pohl
9 The Space Merchants, Frederik Pohl and C.M. Kornbluth
10 Earth Abides, George R. Stewart
11 Cuckoo's Egg, C.J. Cherryh
12 Star Surgeon, James White
13 The Three Stigmata of Palmer Eldritch, Philip K. Dick
14 Radix, A. A. Attanasio
15 2001: A Space Odyssey, Arthur C. Clarke
16 Ringworld, Larry Niven
17 A Case of Conscience, James Blish
18 Last and First Man, Olaf Stapledon
19 The Day of the Triffids, John Wyndham
20 Way Station, Clifford D. Simak
21 More Than Human, Theodore Sturgeon
22 Gray Lensman, E.E. "Doc" Smith
23 The Gods Themselves, Isaac Asimov
24 The Left Hand of Darkness, Ursula K. Le Guin
25 Behold the Man, Michael Moorcock (Definitely not for the orthodox Catholics among us.
26 Star Maker, Olaf Stapledon
27 The War of the Worlds, H. G. Wells
28 20,000 Leagues Under the Sea, Jules Verne
29 Heritage of Hastur, Marion Zimmer Bradley
30 The Time Machine, H. G. Wells
31 The Stars My Destination, Alfred Bester
32 Slan, A. E. Van Vogt
33 Neuromancer, William Gibson
34 Ender's Game, Orson Scott Card
35 In Conquest Born, C. S. Friedman
36 Lord of Light, Roger Zelazny
37 Eon, Greg Bear
38 Dragonflight, Anne McCaffrey
39 Journey to the Center of the Earth, Jules Verne
40 Stranger in a Strange Land, Robert A. Heinlein
41 Cosm, Gregory Benford
42 The Voyage of the Space Beagle, A. E. Van Vogt
43 Blood Music, Greg Bear *
44 Beggars in Spain, Nancy Kress*
45 Omnivore, Piers Anthony
46 I, Robot, Isaac Asimov
47 Mission of Gravity, Hal Clement (Wake me when it's over)
48 To Your Scattered Bodies Go, Philip Jose Farmer
49 Brave New World, Aldous Huxley
50 The Man Who Folded Himself, David Gerrold (Really? Must Reads?)
51 1984, George Orwell
52 The Strange Case of Dr. Jeckyl And Mr. Hyde, Robert Louis Stevenson
53 Snow Crash, Neal Stephenson
54 Flesh, Philip Jose Farmer
55 Cities in Flight, James Blish
56 Shadow of the Torturer, Gene Wolfe
57 Startide Rising, David Brin
58 Triton, Samuel R. Delany
59 Stand on Zanzibar, John Brunner
60 A Clockwork Orange, Anthony Burgess
61 Fahrenheit 451, Ray Bradbury (The bleak Francois Truffaut film is a must)
62 A Canticle for Leibowitz, Walter M. Miller Jr.
63 Flowers for Algernon, Daniel Keyes*
64 No Blade of Grass, John Christopher
65 The Postman, David Brin
66 Dhalgren, Samuel R. Delany (Pretentious rip-off of Finnegan's Wake device)
67 Berserker, Fred Saberhagen
68 Flatland, Edwin Abbott Abbott
69 Planiverse, A. K. Dewdney
70 Dragon's Egg, Robert L. Forward
71 Downbelow Station, C. J. Cherryh
72 Dawn, Octavia E. Butler
73 The Puppet Masters, Robert A. Heinlein (You've basically seen this as a Star Trek episode)
74 The Doomsday Book, Connie Willis
75 Forever War, Joe Haldeman
76 Deathbird Stories, Harlan Ellison
77 Roadside Picnic, Arkady Strugatsky
78 The Snow Queen, Joan D. Vinge
79 The Martian Chronicles, Ray Bradbury
80 Drowned World, J.G. Ballard
81 Cat's Cradle, Kurt Vonnegut
82 Red Mars, Kim Stanley Robinson
83 Upanishads, Various (Though I don't like the idea of any group's sacred works being regarded as Science Ficiton. I'd say the Book of Mormon and Doctrines and Covenants comes a whole lot closer.
84 Alice in Wonderland, Lewis Carroll*
85 The Hitchhiker's Guide to the Galaxy, Douglas Adams
86 The Lathe of Heaven, Ursula K. Le Guin (Along with He Who Shapes, by Zelazny, a remarkable exploration of the life of the mind)
87 The Midwich Cuckoos, John Wyndham (Great 60s SF flick, don't recall the name, something like Children of the Damned)
88 Mutant, Henry Kuttner
89 Solaris, Stanislaw Lem
90 Ralph 124C41+, Hugo Gernsback (Truly tiresome, but very important for a STUDENT of SF)
91 I Am Legend, Richard Matheson
92 Timescape, Gregory Benford
93 The Demolished Man, Alfred Bester
94 War with the Newts, Karl Kapek (Not R.U.R.?)
95 Mars, Ben Bova
96 Brain Wave, Poul Anderson
97 Hyperion, Dan Simmons
98 The Andromeda Strain, Michael Crichton
99 Camp Concentration, Thomas M. Disch
100 A Princess of Mars, Edgar Rice Burroughs
