I would recommend

_The Hitchhiker's Guide to the Galaxy_	by Douglas Adams
_Time And Stars_			by Poul Anderson
_Fantastic Voyage_			by Isaac Asimov
The "Foundation" trilogy		by Isaac Asimov
_The Caves of Steel_			by Isaac Asimov
_I, Robot_				by Isaac Asimov
_The Player of Games_			by Iain Banks
_The Demolished Man_			by Alfred Bester
_Brightness Reef_			by David Brin
_Infinity's Shore_			by David Brin
_Magic Kingdom, For Sale.. Sold!_	by Terry Brooks
_Tangle Box_				by Terry Brooks
_Yendi_					by Steven Brust
_The Phoenix Guards_			by Steven Brust
_Brothers in Arms_			by Lois McMaster Bujold
_Mirror Dance_				by Lois McMaster Bujold
_Cetaganda_				by Lois McMaster Bujold
_A Civil Campaign_                      by Lois McMaster Bujold
_The Curse of Chalion_                  by Lois McMaster Bujold
_Ender's Game_				by Orson Scott Card
_Lest Darkness Fall_			by L. Sprague de Camp
_The Dragon Never Sleeps_		by Glen Cook
The Annals of the Black Company		by Glen Cook
_Do Androids Dream of Electric Sheep?_  by Philip K. Dick
The "Gap" cycle				by Stephen Donaldson
_Axiomatic_                             by Greg Egan
_Neverwhere_                            by Neil Gaiman
_A Wizard of Earthsea_			by Ursula le Guin
_The Tombs of Atuan_			by Ursula le Guin
The Night's Dawn Trilogy                by Peter F. Hamilton
_Tuf Voyaging_				by George R. Martin
_Dragonflight_				by Anne McCaffrey
_The Last Dancer_			by Daniel Keys Moran
_The Long Run_				by Daniel Keys Moran
_The Mote in God's Eye_			by Larry Niven/Jerry Pournelle
_Protector_				by Larry Niven
_The Anubis Gates_			by Tim Powers
_On Stranger Tides_			by Tim Powers
_Santiago_                              by Mike Resnick
The Harry Potter Series                 by J.K. Rowling
_With a Strange Device_			by Eric Frank Russell
The "Lensman" Series			by E.E.'Doc' Smith
_The Green Pearl_			by Jack Vance
_The Peace War_				by Vernor Vinge
_Marooned in Realtime_			by Vernor Vinge
_A Fire Upon the Deep_			by Vernor Vinge