Since I'm an rpg fan, I'd have to go with either NIS or Monolith Software.
Monolith Software has this team of genius who gave us extremely long, complete and cultivated games like Xenosaga and Baten Kaitos for example.
On the other hand, NIS are good at breaking any limits previously established by the industry in terms of novelty, originality and gameplay. Just think about the fact that you can level your characters up to 9999, or deal billions and billions of damage to opponents or even lift houses with you bare hands and throw them away. Plus, they get to make you laugh with silly randomness, and on that topic, I'd like to close that post with a ZETA BEAM!!
In the later leg of 2008, it was valve. Then i got halo 3 in March, then Bungie took the show for a while. Then DICE ahnilated Halo's asshole with 1943 and BFBC franchise. And most recently, Bungie, again. I was indeed Reaching for a way back to Bungie. wink wink.
My favorite video game company was Pandemic, but they got bought out so now it's either Media Molecule or Insomniac since. I enjoy playing LittleBigPlanet made by MM with my friends yet Insomniac's Ratchet and Clank got me into gaming.