I explored the Internet and discovered over a dozen lists of Best Science Fiction Books, then compiled them into one large meta-list. The results are below: every book (or series) that was listed on at least three of the original source lists.  I have organized them in rank order, with the books that are on the most lists at the top.  Books on the same number of lists are organized in chronological order.  If the entire series is listed, I have also included the name of the first published book in the series. I have also made a list of the Best Fantasy Books, which you can find HERE.

On 10 lists of Best Science Fiction Books
Neuromancer (1984). By William Gibson (US/Canada).

On 9 lists
The Forever War (1974). By Joe Haldeman (US).
The Hitchhiker’s Guide to the Galaxy (1979). By Douglas Adams (UK).
Snow Crash (1992). By Neal Stephenson (US).

On 8 lists
Dune (1965). By Frank Herbert (US).
The Left Hand of Darkness (1969). By Ursula K. LeGuin (US).
Ender’s Game (first in Ender’s series, 1985). By Orson Scott Card (US).
Contact (1985). By Carl Sagan (US).

On 7 lists
A Canticle for Leibowitz (1960). By Walter M. Miller, Jr. (US).
The Moon Is a Harsh Mistress (1966). By Robert Heinlein (US).
Ringworld (first in series, 1970). By Larry Niven (US).

On 6 lists
The Time Machine (1895). By H.G. Wells (UK).
The War of the Worlds (1898). By H.G. Wells (UK).
Brave New World (1932). By Aldous Huxley (UK).
Nineteen Eighty-Four (1949). By George Orwell (UK).
Childhood’s End (1953). By Arthur C. Clarke (UK).
The Stars My Destination (1957). By Alfred Bester (UK).
Slaughterhouse-Five (1969). By Kurt Vonnegut (US).
The Dispossessed: An Ambiguous Utopia (1974). By Ursula K. LeGuin (US).
The Handmaid’s Tale (1985). By Margaret Atwood (Canada).
The Diamond Age: Or, A Young Lady’s Illustrated Primer (1995). By Neil Stephenson (US).
A Fire Upon the Deep (1992). By Vernor Vinge (US).
Red Mars (first in the Mars trilogy, 1993). By Kim Stanley Robinson (US).

On 5 lists
Frankenstein; or, The Modern Prometheus (1818). By Mary Shelley (UK).
Twenty Thousand Leagues Under the Sea (1870). By Jules Verne (France).
I, Robot (short stories, 1950). By Isaac Asimov (US).
The Martian Chronicles (short stories, 1950). By Ray Bradbury (US).
The Foundation Trilogy (first three books in series, 1951-1953) (first book: Foundation (1951)). By Isaac Asimov (US).
Fahrenheit 451 (1953). By Ray Bradbury (US).
Stranger in a Strange Land (1961). By Robert Heinlein (US).
A Clockwork Orange (1962). By Anthony Burgess (UK).
The Man in the High Castle (1962). By Philip K. Dick (US).
Flowers for Algernon (short story 1959, novel 1966). By Daniel Keyes (US).
2001: A Space Odyssey (1968). By Arthur C. Clarke (UK).
Stand on Zanzibar (1968). By John Brunner (UK).
The Mote in God’s Eye (1974). By Larry Niven & Jerry Pournelle (US).
Altered Carbon (2002). By Richard K. Morgan (UK).

On 4 lists
The Day of the Triffids (1951). By John Wyndham (UK).
I Am Legend (1954). By Richard Matheson (US).
The Sirens of Titan (1959). By Kurt Vonnegut (US).
Starship Troopers (1959). By Robert Heinlein (US).
Solaris (1961). By Stanislaw Lem (Poland).
Cat’s Cradle (1963). By Kurt Vonnegut (US).
Do Androids Dream of Electric Sheep? (1968). By Philip K. Dick (US).
Ubik (1969). By Philip K. Dick (US).
Rendezvous with Rama (1973). By Arthur C. Clarke (UK).
Hyperion (first in Hyperion Cantos series, 1989). By Dan Simmons (US).
Use of Weapons (from the Culture series, 1990). By Iain M. Banks (UK: Scotland)
Revelation Space (first in series, 2000). By Alastair Reynolds (UK).
American Gods (2001). By Neil Gaiman (UK).
Old Man’s War (first in series, 2005). By John Scalzi (US).
The Road (2006). By Cormac McCarthy (US).
Anathem (2008). By Neal Stephenson (US).
The Windup Girl (2009). By Paolo Bacigalupi (US).

On 3 lists
A Journey to the Center of the Earth (1864). By Jules Verne (France).
The Demolished Man (1953). By Alfred Bester (US).
The Caves of Steel (1954). By Isaac Asimov (US).
A Wrinkle in Time (first in the Time series, 1962) by Madeleine L’Engle (US).
Lord of Light (1967). By Roger Zelazny (US).
Dragonriders of Pern (series, 1968 and continuing) (first book: Dragonflight (1968)). By Anne McCaffrey (some books authored or co-authored by Todd McCaffrey).
Roadside Picnic (1971). By Arkady and Boris Strugatsky (USSR)
To Your Scattered Bodies Go (first in the Riverworld series, 1971). By Philip José Farmer (US).
The Gods Themselves (1972). By Isaac Asimov (US).
The Female Man (1975). By Joanna Russ (US).
Dhalgren (1975). By Samuel R. Delany (US).
Lucifer’s Hammer (1977). By Larry Niven & Jerry Pournelle (US).
Gateway (first in the Heechee Saga series, 1977). By Frederik Pohl (US).
The Book of the New Sun (series, 1980-1983) (first book: The Shadow of the Torturer (1980)). By Gene Wolfe (US).
Speaker for the Dead (from the Ender’s series, 1986). By Orson Scott Card (US).
The Player of Games (from the Culture series, 1988). By Iain M. Banks (UK: Scotland).
Doomsday Book (first in series, 1992). By Connie Willis (US).
The Farseer Trilogy (series, 1995-1997) (first book: Assassin’s Apprentice (1995)). By Robin Hobb (US).
The Reality Dysfunction (first in The Night’s Dawn trilogy, 1996). By Peter F. Hamilton (UK).
Pandora’s Star (from the Commonwealth Saga, 2004). By Peter F Hamilton (UK).
The Hunger Games (first in trilogy, 2008). By Suzanne Collins (US).
The Three-Body Problem (first in Remembrance of Earth’s Past trilogy, 2008). By Liu Cixin (China).
The City and the City (2009). By China Miéville (UK) (also listed as Fantasy).
Ancillary Justice (first in series, 2013). By Ann Leckie (US).