I don't think anyone really knows. Usually there is someone who rises up. From what I remember, nobody would have thought Bush jr. would be the nomination in 1996.
I don't think Hillary will get the Democrat nomination, because alot of them are probably going to start resenting the Clintons hijacking their party just for their own personal gain. I know alot of Democrats didn't appreciate the old Clinton team's handling of Kerry, and there was some conflicts.
As for Obama, the Republicans wouldn't have to mention his race. They just show his smiling face in their ads, and all those southern states stay red (plus probably some of those nice blue NE states).
And I have no idea where the Republicans go. Cheney will be put back in deep-freeze for the next time hippies need to be put in their places
, Powell (who seems like he could beat anyone at this point, even after the UN fiasco) doesn't seem to want it (and does anyone know if he's staying as Sec of State? I had heard he was leaving after the election), and McCain will be fairly old by then. Maybe Rudy, but his personal baggage might be alot to overcome, plus it might be hard to keep his name around, unless he can get some office quick.