I recently went through some of the recent winners of the Arthur C Clarke award, as a good starting point for modern sci-fi.
Air, by Geoff Ryman was really good, about a remote village coming to grips with new technology, told from the viewpoint of an illiterate woman.
Perdido Street Station by China Mieville is more on the fantasy side. Can't describe it but intelligent, scary, inventive and well worth a read.
Agree with Cote Neal Stephenson is god. The Diamond Age, Snow Crash, Cryptonomicon are all fabulous, as is the Baroque Trilogy, though don't know if that's strictly sci-fi.
Some classics worth a read for me: The Man In The High Castle by Philip K Dick, a what if scenario had the Germans and Japanese won the 2nd World War; Stand on Zanzibar by John Brunner, a brilliant portrayal of an overpopulated future earth running out of resources; More Than Human by Theodore Sturgeon.
Ursula K. Le Guin crosses both sci-fi and fantasy camps, I read loads of her stuff as a teenager and keep meaning to go back to it.