Ian Douglas, the Heritage Trilogy (and there's a second trilogy out now as well). VERY nice sci-fi, based around the Marine Corp.
I've read (and own) literally everything by William Gibson except the newest release. Neuromancer is a prime classic. Neal Stephenson's Snow Crash, The Diamond Age, and Cryptonomicon (while not really sci-fi, is very tech oriented and wonderful) are must reads.
Richard K. Morgan's Takeshi Kovacs novels are a wonderful new find. I've gotten hooked on them, thanks to my library. Very cyberpunk, total action, good stuff.
Asimov and Heinlein are of course essentials.
However, on the difficult to find, but WELL worth the search, list ....
John Shirley, A Song Called Youth trilogy. These Are Absolutely Fabulous. Eclipse, Eclipse Penumbra, and Eclipse Corona are mindblowingly fabulous, especially if you're into serious hard sci-fi.