I think that Romney’s the only one who is definitely running, but it’s hard to tell with the rest. I wouldn’t be surprised if there’s an under-the-table gentlemens’ agreement to avoid declaring for a long time in order to shorten the primary season; the common wisdom is that a long and combative primary process damages candidates for the general election. (The Obama-Clinton primary would argue against this, though.) I think Gingrich will run, as will Huckabee, though both would retain credibility. John McCain seems to have given up; he took heat for being so old in 2008, and I simply don’t think he’d be a very credible candidate for the simple fact of his age.
Palin, I think, will run for the sake of maintaining her credibility as someone important. A half-term governor of Alaska simply can’t be taken that seriously for that long unless she can keep herself in politics. Running will keep her in the public eye, which is what her job is now. Should she run for President, I suspect she’ll drop out early and keep getting her big checks from Fox News.
Right now, I’d put the odds on Obama winning at 3 to 2. I think he has an edge as the incumbent, but not a huge edge.