As I am a big for sci-fic, anything by Stephan Baxtar, notably Raft, The Ring, The Timeships, and the Manifold series. Can be a little hardcore, but incredibly thought provoking stuff. The Nights Dawn trilogy by Peter F. Hamilton. Gets a little wacky toward the end, but a great story with enough science to stop it getting way out of hand. Anything by Vernor Vinge is also great, especially A Deepness in the Sky. The Ender Wiggin Saga by Orson Scott card is also intruiging, especially if you have any interest in psychology. If you like your sci-fi with a military bent, you can't go past David Drake. Cross The Stars and Red Liners were great! The Wreck of the River Of Stars, by Michael Flynn. A rich, if somewhat depressing story, of the lives of the crew of a converted stellar sail ship. Centered on the humanistic, yet again with the science (bring on the science!)... Worthwhile reading. To be honest, I have read so much sci-fi over the years, I actually find it difficult to seperate individual books from the clutter in my head. :D