I don't think Gulliani would run for President. VP, maybe, but not POTUS.
I'd look for a Republican primary including Frist, McCain, and possibly Jeb as the heavyweights. it's hard to predict who'd win the primaries, though, since the Republican party could undergo a major change in the next 4 years, especially if GW loses tomorrow.
For the Democrats, assuming Kerry loses... Hillary is the front-runner if she wants it. But despite all the speculation, I wouldn't be suprised if she didn't want it. I'd also expect a reappearence of John Edwards and Jon Corzine (especially if decides not to take over as NJ Governor, and choses instead to stay in Federal politics)