I'm surprised a thread with an OP like this turned into a somewhat serious discussion.
I'd say these are the only possible options at the moment:
Sicker Punch - Make great games, and Infamous 2 is looking a step above their usual work. however, Sony has been working with them for over a decade, and they haven't been bought yet, which implies they favor independence. And it's not like they need to buy them anyway. I wish it would happen, though, as I think it's he only way they'd finally increase they're team size, increasing their output rate.
Quantic Dream - Not likely to happen. Yeah, they have a deal with Sony at the moment, but from what I understand they're larger than just a development studio (though I'm not sure what else they do. license mocap tech?). Also, David Cage seems like the type of guy that'd never give up the reigns of his company now matter what deal was offered.
Honestly though, I'd want them to make some moves on the Japanese front. I used to think From Software would be an awesome choice, but what with the whole Demon's Souls fiasco, that's looking less likely than ever.
They should at least form some new deals with third parties over there (I feel Platinum Games was a big missed opportunity on their part), or found a new studio in another city, redubbing Japan Studio as Tokyo Studio.
Given the climate in Japan, I think founding a new studio would be looked upon better than buying somebody else, which may be why they're averse to doing so, but it's hard to start a studio without manpower, and that seems like something somewhat hard to come by in the Japanese industry today.
