I think there are plenty of books to come off this list before Ender's Game. It is one of the best Young Adult sci-fi books.
Not my fault it's at the top of the list.
Orson Scott Card Ender's Game (2) -1Frank Herbert Dune (4)
Douglas Adams Hitch Hiker's Guide to the Galaxy ( 6 )
George Orwell 1984 (2)
Robert A Heinlein Stranger in a Strange Land (3)
Isaac Asimov I, Robot (2)
William Gibson Neuromancer (3)
Philip K Dick Do Androids Dream of Electric Sheep? ( 4 )
Aldous Huxley Brave New World (1)
Robert A Heinlein The Moon is a Harsh Mistress (4)
H G Wells The War of the Worlds (3)
Arthur C Clarke Childhood's End (1)
Dan Simmons Hyperion (4)
Joe Haldeman The Forever War ( 1 )
Kurt Vonnegut Slaughterhouse Five ( 3 )
Daniel Keys Flowers For Algernon ( 4 )
Philip K Dick The Man in the High Castle ( 5 )
Frederik Pohl Gateway ( 4 )
C.J. Cherryh Cyteen ( 5 ) +1Robert A Heinlein Citizen of the Galaxy ( 7 )
China Mieville Perdido Street Station ( 4 )
Alfred Bester The Stars My Destination ( 5)
Alfred Bester The Demolished Man ( 4 )
Stanislaw Lem The Cyberiad ( 3 )
Arthur C Clarke 2001: A Space Odyssey (0)
H G Wells The Time Machine (0)
Orson Scott Card Speaker for the Dead (0)
Neal Stephenson Snow Crash (0)
Ursula K Le Guin The Left Hand of Darkness (0)
Ray Bradbury Fahrenheit 451 (0)
Arthur C Clarke Rendezvous With Rama (0)
Larry Niven Ringworld (0)
Isaac Asimov Foundation (0)
Isaac Asimov The Caves of Steel (0)
Ray Bradbury The Martian Chronicles (0)
Robert A Heinlein Starship Troopers (0)