Democrats
-Montana Gov. Brian Schweitzer (for 2012), New York Gov. Eliot Spitzer (if he wins next year -in which case, he will be the main candidate for 2016 once he completes two terms, if he wins them),
and Illinois Sen. Barack Obama in 2016.
Republicans
-South Carolina Gov. Mark Sanford, Minnesota Gov. Tim Pawlenty. i can't think of anymore at this time.
I would love to see Shweitzer run, but he is to conservative to get the democratic nomination(pro-gun and fiscally responsible) unless the dems loose in 08 and get really desperate.