Big question...

Kim Stanley Robinson - Mars Trilogy, Science in the Capital series, Antarctica
Neal Stephenson - Anathem, Snow Crash, The Diamond Age
Ken MacLeod - Fall Revolution series, Execution Channel
Robert Heinlein - Podkayne of Mars, Moon is a Harsh Mistress, Starship Troopers
Sean McMullen - Greatwinter series
Joe Haldeman - The Forever War
Connie Willis - Doomsday Book
Ursula K. LeGuin - The Dispossessed and The Left Hand of Darkness
William Gibson - Neuromancer, The Bridge Trilogy, and the Blue Ant books
Iain Banks - Consider Phlebas
Samuel Delany - Dhalgren
Maureen McHugh - China Mountain Zhang
Nicola Griffith - Ammonite
Pat Murphy - The City, Not Long After
Frank Herbert - Dune
Arthur C. Clarke - Childhood's End, Rendezvous with Rama
David Brin and Gregory Benford - Heart of the Comet
David Brin - Startide Rising
Walter M. Miller, Jr. - A Canticle for Leibowitz
N. K. Jemisin - The Fifth Season
Charles Stross - Halting State
C.J. Cherryh - Downbelow Station
Larry Niven - Ringworld, Protector
Larry Niven and Jerry Pournelle - The Mote in God's Eye

There are some books I'm not sure I fully consider science fiction and so hesitate to recommend in this context - like Connie Willis' "To Say Nothing of the Dog" (even "Doomsday" felt a bit of a stretch) or "Hitchhikers Guide to Galaxy" or China Mieville's "The City & The City." And there's a couple books that would have been on here, but their authors' views on some social and political matters make them impossible to recommend.