The answer for myself is essentially a "who's who" list of some of my favorite developers from this generation. (This seems to be the case with a lot of responses in this thread.)
Naughty Dog, Insomniac, Sucker Punch: All three of these developers have done world-class platform games. I'm curious to see if they'll be cooking up more platformers in the future, or if they'll bring their talents to other genres.
Polyphony Digital: The Gran Turismo series is still the king of racing simulations. With all the effort they pour into each successive installment, the future of the series is going to be spectacular.
Criterion: Burnout 3 isn't just a game--it's a preview disc of next generation gaming.
Snowblind Studios: The new "Champions" of action role-playing games. I generally despise most console RPGs, but these guys have actually made RPGs that are not just graphically impressive, but fun, too.
Harmonix: Their games are highly creative and highly enjoyable.
Digital Eclipse: Their emulations of classic video games are almost always very high quality. I know they've got Death, Jr. in the works for PSP, but will they also be working on classic game compilations for that system? Let's hope so!
Llamasoft: Tempest 2000 and Tempest 3000 were ace. If Jeff can ever finish up Unity, then maybe Atari could hire him to do an all-new Tempest game on PSP (wishful thinking, I know).