Naughty Dog too?

Yep, they fell from grace after the disappointing Jak II and III. Uncharted didn't help them along either.

I actually wanted to say Sucker Punch as I have liked all their games, but I wasn't sure if we were allowed to mention 2nd parties 

Naughty Dog & Poliphony for PS3...

Sony--Naughty Dog with Santa Monica trailing for a close second.

Microsoft--Used to be Bungie but right now I would say Rare....And I have a feeling 343 studios will be the most important once they start releasing games.

Nintendo--whatever studio Myamoto works for.

Nintendo's most valuable development house is Nintendo EAD by far. Those of you saying Retro don't have any idea about what you are talking about, and I'll tell you why:

Nintendo EAD is the segment run by Shigeru Miyamoto (and Tezuka Takahashi). It consists of 7 branches responsible for the development of different sets of franchises. These franchises include: Wii Sports, Wii Fit, Mario Kart, Super Mario, Legend of Zelda, Nintendogs, and other core-Nintendo franchises. These franchises combined have sold in the hundreds of millions just thig generation alone; 11 of their releases have shipped over 20 million units. Keep that "11 games have shipped over 20 million this generation" figure in mind because in the 12 and a half years Retro has existed, they have sold a total of 10 million copies; that is 10 million units shipped by Retro vs 11 games that have shipped 20 million or more by Nintendo EAD.

Sony, MS = Activision

Nintendo= Nintendo

in all seriousness, i would have to go with ND

although i still think Guerrilla has made the most advanced engine to date (on consoles)

Microsoft = at the time was bungie but now it is Rare because they made the avatars , the dashboard , they made like 6 games this generation so far i think or 7 idk and helped out with kinect 

sony = santa monica

nintendo =Ead toyko

@ op yea there was a rumour that santa monica where helping london studios with the getaway and 8 days.

sony: I think its naughty dog.  after slim, price cut and proper advertising uncharted 2 kind of sealed the deal that playstation was back. that is the way I saw it anyway.

Microsoft: so far it most likely bungie but probably not anymore, not sure who is next probably a third/second party developer though. they same to be depending a lot on them lately.

edit: I have always liked lionhead and felt microsoft are very lucky to have them.  fable games are one the games I am most interested in and never played on the xbox and in general. they are also doing some interesting stuff with kinect so I think it might be lionhead.

Nintendo: don't know enough about them to be honest.

Come on people, you don't know Sony if you don't think Polyphony digital is their most valuable developer. It's not even close.