Tor Books, which is part of Macmillan
Ballantine Books (and Del Rey), which is part of Random House
Orbit Books, which is part of Little, Brown
Also, for novellas, I am a big fan of PS Publishing (a small, but very respected, British publisher).
The only other big one I can think of is Baen Books, but the only books I am very familiar with from them are science fiction. They do publish fantasy, though. And, of course, Penguin, Simon & Schuster, and HarperCollins all have small imprints for SFF (or else just accept SFF in general), but few of the imprints are big name on their own (unlike the above mentioned). Still, all respectable publishing houses and some good authors attached to each of them.