Maybe Sens. Dorgan, Durbin or Landrieu for the Dems,
For the Reps, Govs. Fletcher or Barbour could emerge if Sanford doesn't run, or Sen. Thune, although he would only have been in the Senate for 4 years (+6 years of house expereince)
If the Democrats nominated Byron Dorgan, that would make my life really, really difficult if the GOP nominates a candidate I'm less than enamoured with. Dorgan seems to have his head screwed on right on several important issues, and recently made a superb speech ripping unfettered free trade to shreds - the first time I've seen any Senator do so on the Floor. I'm sure that if I looked more closely at his record, I'd find things that are objectionable - but at first impressions, he seems like a good candidate for the other party. But, as Thomas Reed said, "they could do a lot worse, and I suspect that they will".
There was a suggestion made on another board that Gov. Napolitano (Ariz.) would, or should, run for the Dems; on the GOP side, I think that the surprises will be in terms of who
doesn't run, as the presumption at this point should surely be that
everyone is going to run. This may be a blandly obvious statement, but I think that the more people that run in the '08 GOP primary, the less predictable it will become, as the votes will split between many candidates. This means that the recently commonsense law of primary physics - that a moderate can't win - may be suspended.