Alistair Reynolds - House of Suns - I can't recommend this one enough.

Dan Simmons - Illium duology & the Endymion & Hyperion books - massive, sprawling, full of dictionaria, though I prefer Illium.

Olaf Stapledon - Last and First Men - an epic, massive work, now almost forgotten.

Philip K. Dick - Valis - this one is whacked out, but Philip K. Dick is quite a classic.

John Scalzi - Old Man's War - an accessible but interesting series. Fuzzy Nation is also fun.

That's all from me for now .