This is just some authors I like: your mileage may vary.
CJ Cherryh's sci-fi burns my brain out, but is good. Highly, -heavily-, psychological, also none of the characters ever gets much sleep (this is starting to piss me off, actually). No humor. I'd recommend Downbelow Station & related books (Hellburner, Heavy Time, Tripoint, Merchanter's Luck - some available in a collected omnibus trade size) the Chanur series, and Cyteen (available in a trade; sequel apparently just released). She's also got about a zillion books in the Pretender/etc/etc series; that's technically sci-fi, but of a different sort.) I've had alot of trouble enjoying her fantasy work, though.
Joe Haldeman - Forever War.
Vernor Vinge - Not as prolific as I'd like, but awesome. 4 Hugos. Rainbow's End; Across Realtime; A Deepness in the Sky; A Fire Upon the Deep (I haven't been able to read, alas).
David Drake's Hammer's Slammers series is good military sci-fi war porn; not deep, but full of tanks that Blow




Up Real Good.
Personally, I think the best thing to do is pick up the Years Best Science Fiction collection (the big, trade paperback one), and if you like a story, look for more by that author. Buy as many as you can, actually - I think they're up to #23 or #24?
I'll post new names if I think of them; most of my sci-fi is in boxes.