Right now, the frontrunner is probably Romney, just because he seems to have the best organization and was "last man standing" against McCain last time around.
That doesn't mean he'll get it, insofar as a lot can happen in the next eight months. Furthermore, his refusal to admit he fucked up with Romneycare will dog him during the nomination process and probably during the general.
Nor does his likely frontrunner status mean that he's my favorite (I'll support him over Obama but that's not saying much). I like Mitch Daniels (who hasn't formally announced) but he's probably not "Jesusy" enough for some of the southern states.
I'm still not convinced Palin is running. I suspect that--like Trump and Huckabee--she's going to figure out that she's got a cushy TV gig and stay put. Furthermore, if Bachmann is getting in I have a feeling that could because Michelle knows Sarah isn't in it. They're allies and I would think that Bachmann would endorse Palin if she was running, instead of running herself.
Newt, god bless him, is probably the smartest guy in either party running. But his personal life will kill him with the religious types and he's probably too much of a technocrat to really resonate with voters.
Keep an eye on Tim Pawlenty. There are some theories that the other candidates will knock each other out and he'll be the compromise candidate.
It's also too early to tell how strong a candidate Obama will be. Yes, he'll have the center-left media, the unions and ACORN stealing every vote they can. And right now he's has some good will from Osama. But things could go sour (again) for him really quick. Or he could catch a break and be even stronger.
However, assuming that Obama is unpopular the "vote for the other guy" theory could get the GOP in regardless of who they run.
No one should be assuming the outcome on either side at this point.
