Robots Spaceships Foundation
The Foundation saga
Asimov was a genius - literally. Anaturalised American (from Russia), he was a prodigy in science and scien fiction.
Asimov was a fantastically prolific author (and not just of Sci-Fi). If you've never rad his stuff, you're in for a treat! Start with the Robot books - they're brilliant, and as anyone will tell you, Asimov was the one who invented the laws of robotics when the science was in its infancy. These books are the best of his output - they'll blow you away. OK, next, read his Galactic Empire stuff - dated, but still fun. Then... the Foundation books - what a trip! This is epic, totally engrossing Sci-Fi. You'll love it.
I was a schoolboy with a thirst for all things Sci-Fi (with the exception of Van Voigt, whom I found somewhat dull and dated). I first read soem of Asimov's short stories and was hooked - as you will be!
The Illustrated Man
If you've never read Ray Bradbury, go out and buy all his early stuff (I reckon he's gone off in recent years). He has a poetic style of writing that screams of a brilliant writer. In fact, the way he uses punctauation to set pace is second only to Shakespeare!