Beyond that, I think the GOP bench is deeper than anyone suspects for 2008. Jeb Bush is out. Even Giuliani will likely be passed over (or, more likely, he will take a pass). Condi Rice is a total long shot. Bill Frist is an unlikely choice; 2004 has reinforced the Senate curse. Look for Bill Owens or Mitt Romney as the odds on favorites, particularly Mitt. A Republican who can win in Massachusetts without being a Bill Weld clone is a guy with serious f*cking chops.
On the Dem side, as I noted, the Senate curse rides on. Look for this to dampen Hillary's chances. Obama, as you mention, is another story, a likely VP candidate for sure. As I've written in the past, I don't think the Dems can keep a minority off the ticket again. Blacks have become such an important part of the party base (cf. Man Without Qualities, here), and holding Hispanics and women has become so difficult, that the Dems need a stunt (no slight to Obama, who seems like a smart and gifted, though wrong on the issues, politician) to keep the masses on the reservation. That alone might pressure a "Draft Condi" movement, or a feeling that Ohio SecState Ken Blackwell handled his 15 minutes in '04 rather, er, well . . . better than Katherine Harris, and she got elected to Congress in '02. Who knows? We might see a sudden minority-on-the-ticket arms race.