I like Obama, I might even vote for him, but not this election. He should stay in the Senate for at least another term. He has nothing to risk. He popular, and he is in a Blue state. He simply just doesn't have enough experience right now, especially in Foreign affairs. The person sitting in the White House currently is case in point about putting someone in office who doesn't have enough experience in Global matters. I don't think we can afford a repeat of that mistake. But he's young, he can run again.
Unfortunately, I also suspect that certain areas of American society may not be ready for a Black President or for a woman for that matter. So that might count as a strike against him.
As for me, I was relatively impressed with John Edwards plans for Universal Heath Care I think it might have merit, so right now I am going with him.
Missileer mentioned Hillary. While she certainly has the cash, I am not sure she as shoo-in as people might think. In terms of popularity I think Obama and Edwards (especially in the South, which is an important inroad for Dems).
Same goes for McCain. He hardcore backing of Bush's Iraq policy cost him a lot of moderate voters (such as myself). Moderates are more likely to support Guiliani than McCain.
McCain and Guiliani are polar opposites. McCain is very likable but his policies are so-so. Guiliani is a nasty guy (not an exaggeration, just ask any NYer) but he is actually very competent. Even so, I still voted for him. So I guess if Chuck Hagel is out my next line of support for Republican Nominee goes to Guiliani.