Isn't Infinity Ward a subsidiary of Activision? Why would they sell? And even if Nintendo purchased Infinity Ward, why would it assign them Metroid Prime 4? Nintendo already has a team that has a successful track record with Metroid Prime -- which isn't a shooter anyway. Nintendo would do much better to scoop up former employees of Eurocom. They have lots of experience with first-person shooters, and a long history with Nintendo.

I have one more. Wayforward, the creators of Mighty Switch Force and Shantae (I think).

Level 5

I'm already liking some of the options people are putting forward.

Eurocom would be a good choice. Platinum Games and Mistwalker are both strong options (although Mistwalker doesn't really do game development, they do the story and concepts). Shin'en is an interesting option, but since they're already pretty much Nintendo-exclusive developers, it wouldn't be worth a whole lot.... but Frozenbyte is definitely a good idea. And WayForward is another interesting idea.

How about 5th Cell?

Vanpool. They're the guys and gals who made the Tingle RPG on DS (a real gem, not being sarcastic), and Dillon's Rolling Western on the 3DS eshop, among having contributed on other stuff like Little King's Story, WiiPlay Motion and Mario & Luigi on GBA. I'm thinking they could become a real great dev under Nintendo, and they have a really quirky and unique vision of how to make fun and interesting games.

Shin'en would be a good bet too, though they're currently already practically a Nintendo 2nd party anyway. :p They're consistenly putting out quality stuff for Nintendo's platforms.

Vigil might be a good one as well. They could very well become something like Retro, under Nintendo. Clearly they have (had) some very talented people and interesting ideas. They seem really fond of Nintendo, too.

As others have suggested, HVS would make an interesting candidate too. I think as an independent dev they're really struggling to turn their visions and ideas (which seem to be great) into full games, having to deal with very limited budgets and deadlines, as well as lacking a publisher. Nintendo owning them could really help them out a lot, I should think. Them being really devoted to and excited by Nintendo themselves would seem like a plus, too.

Actually, Nintendo could also take Level-5 with open arms, as suggested by Jumpin. Level-5 has been supporting the 3DS quite well from launch to now.

None.

The reason I say this is because we've been told many times that Nintendo has its own way to aproach game development, a way that's not exportable to every studio. What if Ninty buys a studio but after a few months people leave because they don't want to/can't adapt to the new work philosophy? All that money would have been wasted.

If Nintendo wants to increase their dev teams, which should, the better way of doing that would be either creating new studios from the ground or by hiring people to expand their existing studios so they can produce more games.

I'm sure Nintendo has already hired people from other studio closures to increase and improve their dev teams.

Nintendo doesn't have to force major changes in studios.

Rare

The main thing is vigil can be bought on the cheap now. Thought it might be too late already, im not sure.

Rare im pretty sure Nintendo wanted, but Microsoft is not gonna sell now that they make huge sales on kinect games.