The CW has been that if Hillary won, she wouldn't take Obama or Edwards. I think that's changed.
If Obama wins, you can have a fabulous parlour game of balancing the ticket by race/age/region.
McCain I think would take Huckabee as sop to the evangelicals, unless he's committed to someone like Tim Pawlenty or something. Ditto Giuliani, I think. Romney would want to balance the ticket, but there's been some blood spilt.
If Huckabee takes the nomination, who knows. He's been endorsed by Chuck Norris, Ric Flair, and Ted Nugent. That's the beginnings of one hell of a cabinet.