Green Ronin While they're not doing a lot of the stuff I'd like to see, they're still doing a few d20 books.
Mongoose just came out with some 'renegade' tomes for clerics and wizards but like GR, mostly OGL and nowadays, miniatures with future plans for Runequest.
Necromancer Games one of the few whose function comes from d20, mainly adventure/sourcebooks with a few jaunts off to pure sourcebooks like Eldritch Sorcery and Tome of Horrors.
Goodman Games another one of the few whose main line seems to be classic dungeon crawl adventurers. Dragon Mech is pretty interesting for those looking for something different.
Privateer Press. is mainly into the miniatures but they still do RPG support in their mag No Quarter and they're supposed to have another Monsternomicon.
Malhavoc still doing some d20 support but seems fractured between AE, IH, and while Ptlous is d20, if it ain't your bag, they got nothing for you. The days of their general D20 support seem over.
White Wolf-Sword and Sorcery mostly out but still doing World of Warcraft and occassional other bits.
Alderac aka AEG and only because their Warlords books are supposed to be out (haven't seen 'em) and World's Largest City is supposed to be coming out. Let's check the web site... gee... nothing. Shocking!
Wizards of the Coast still the big dog.