Nintendo: Platinum Games

Sony: Harmonix

That is all.

Sony: Bethesda or Bioware to push american sales.... i would say Kojima but there doing fine in Japan

Sony : Rockstar

Sony - Level 5 and/or Atlus

Sony need more JRPGs dammit!

EA, or more to the point, Criterion, because I'd dream of a 1st party Burnout!

Sony has already a lot of first-party and second party developers, enough to publish at least 2 or 3 good titles each season, they should work to keep the good shape of what they already have....I prefer Kojima Productions to be indipendent.
1st party titles has never been the microsoft goal for they're console succes, still they should try to attract more eastern developers, to make them more competitive in japan.
Nintendo, is the one who has problems to deliver some good 1st/2nd party game each season and considering all the income from wii and ds in recent years is the one who should try to expand. They should try to buy some small developer, and help them to grow someone like platinum games, free radical, Treasure, Mistwalker or an indie developer like 2D boy, studio pixel or also create a team headed by Jonathan Blow (Braid creator)

i would want sony to aquire insomniac or quantic dream

Nintendo: Sony (to watch the internet explode)
Sony: Nintendo (same reason)
Microsoft: I would be amazed to see them buy anyone and keep their doors open, or able to keep said developer first party. (really man? Closing ensemble aint cool!)

Hmm... I kinda like the idea of Nintendo purchasing Atlus. Or hell, we can also let MS purchase S-E while we're at it.