If there's a strong anti-incumbent sentiment in 2012 it's quite possible that Republicans could lose the House but gain the Senate and Presidency. There are a lot of marginal seats in the House which went Republican during the 2010 wave, and it wouldn't be hard for some of those to switch back. Whereas Democrats in the Senate have a lot more seats to defend than Republicans, and it's generally acknowledged that Republicans are highly likely to gain control of the Senate in 2012, albeit probably not by a filibuster-proof margin.
My current prediction is that Rick Perry will be the next President of the United States. The case for that is pretty straightforward: He is the odds-on favorite to win the Republican nomination (39% to Romney's 30.1% on Intrade), and for good reason. The two main things Republican primary voters are looking for is a solid conservative candidate and an electable candidate, and he fits the bill exactly. Now of course it's possible that Obama may tank so badly by next year that a fried potato could beat him, but Republicans will be looking for someone who can actually win, not just rely on Obama to lose.
Michelle Bachmann is a conservative favorite, but she has no executive experience and only four years in the House; she'll be seen as unelectable. Her campaign is about building up her name recognition for the future. Now having said that, it's almost exactly analogous to Barack Obama's situation in 2007. He had no executive experience and only four years in the Senate, and initially he was running to build up his name recognition for the future. He surprised everyone (probably including himself) by catching fire and winning the Democratic nomination in a year which highly favored the Democrats, especially against a weak Republican candidate. So Bachmann can't be entirely ruled out. But the bad taste left in people's mouths by Obama's lack of executive experience will work against her.
Sarah Palin has an intense core following but even many of her supporters doubt her electability after the past savaging she has endured. She at least has a modicum of executive experience, but quiting in the middle of her term is a huge negative. She's a charismatic speaker, so also cannot be entirely ruled out. But at this point I doubt that she'll even get into the race.
Ron Paul has an intense core following, but little chance of expanding beyond his libertarian base. If he ever got seriously close to the nomination, establishment Republicans would do whatever it took to prevent that from happening. Perhaps the Libertarian Party can persuade him to run again as our candidate. Ditto with Gary Johnson.
Pawlenty has dropped out, and a bunch of other candidates (Bolton, Cain, Gingrich, Giuliani, Huntsman, Johnson, McCotter, Santorum) are in the polling noise with no hope of going anywhere.
That leaves Mitt Romney, who's electable but not conservative enough. "Romneycare" from when he was governor of Massachusetts will hurt him in the primaries (although not in New Hampshire), along with several of his other positions. He's got lots of money, but a somewhat bland personality and a very cautious campaign style. I don't think his Mormonism is a big factor, at least no more than JFK's Catholicism was. Republican might pick Romney as their safe choice if they had no better option available.
Rick Perry will be seen as both conservative and electable. He's never lost an election, and he's been governor of a very large state for eleven years so he has ample executive experience. He can point to a track record of economic growth, job increases, restrained taxes, and reduced government regulations to improve the business climate. Unless he makes a major blunder (unlikely, since he's known as a savvy and effective campaigner) he should win the Republican nomination.
As far as the general election is concerned, it's shaping up as a referendum on Obama (as most contests with an incumbent are). The overarching issues will be unemployment, the economic depression, the federal deficit, and Obamacare. Perry will be able to credibly attack Obama on all these issue, while Obama will be reduced to counterattacking Perry over his Bush-sounding Texas twang and his C and D grades in college. Intrade lists Obama's re-election chances at 52.2%, but that factors in all of the remaining uncertainty about who will get the Republican nomination. Once the primaries get underway and the Republican field narrows down to Romney and Perry, I expect Obama's re-election odds to drop correspondingly.
My guess is that Perry will choose Indiana Governor Mitch Daniels as his VP candidate. That will strengthen him in the midwest, and put the focus of the campaign purely on executive competence and economic recovery. There's also some chance that Perry could choose Marco Rubio as VP, to solidify Florida and make inroads into the Hispanic vote nationwide, but Rubio's lack of experience is a drawback.