Add to the list before the poll goes up if you want.
Here's a decent list of them:
http://en.wikipedia.org/wiki/List_of_vi ... developers
Bethesda Softworks (Oblivion, Fallout)
Bioware (Baldurs Gate, NWN2, Jade Empire, Mass Effect)
Blizzard Entertainment (Lost Vikings

Bungie Studios (Halo)
Capcom (Street fighter, Devil May Cry)
Crytek (Crisis. Far Cry)
Electronic Arts (Maddon, Ultima, Sims)
Epic Games (Gears of War, Unreal)
Firaxis Games (Civilization, Spore)
Funcom (Anarchy Online, Age of Conan, Dreamfall)
Bah, too many of them. Check the link yourselves.
I suppose the question would be, which studio do you look forward to seeing new games from the most? I'm guessing most will say Blizzard. Mine's NCSoft. (Lineage II, Guild Wars, City of Heroes/Villains, Marvel Universe Online) I like their style and they seem to be moving in the right direction. I'm hoping Marvel Universe Online turns out well for the PC and 360.