I'll toss out my suggestions as well
Kim Stanley Robinson: Red Mars, Green Mars, Blue Mars and the Martians. I haven't read these yet (but I do have them): Iceheng and Antarctica; I've yet to buy the California Trilogy. KSR's stories are very, very dense and very political (with a seeming left/liberal slant), and while they are very character driven, it is thick with psychological and scientific descriptions.
Timothy Zahn: Angelmass, Deadman Switch, Icarus Hunt, and Manta's Gift.
TZ's stand alone novels are fun, and fast paced. He gives a very clear sense of the universes he's painting, does a good job fleshing the technology without pervading the story with it, and weaving in the politics of the given universe.
I tried getting into his Conqueror's Trilogy, but it hasn't been as engaging as his standalone novels. If you like Star Wars, then you must, must read TZ's Star Wars novels (and I recommend them in this order if you've never read them: Heir to the Empire, Dark Force Rising, The Last Command, Spectre of the Past, Visions of the Future, Survivor's Quest, Outbound Flight, Allegiance).
Peter David: I'm only familiar with his Star Trek novels, so this is more of a particular taste. But David eschews the typical Trek jargon and favors the characters for the characters' sake, mixing in his trademark smartass humor. I recommend Q-Squared and the New Frontier series.
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