It'll be 3 years until we get close to the answer that this thread asks, but we might as well get started.
GOP
S. Palin (a colossus bestrides the world)
W. "M." Romney
M. Huckabee
N. Gingrich (my perennial favorite)
B. Jindal (already says he's out)
T. Pawlenty
K. Bailey Hutchison
M. Sanford
D. Patreus
T. Ridge (abortion position update alert!!!)
J. DeMint
C. Crist (here's a hint: teh gay)
R. Paul
A. Keyes
J. Bush
R. Giuliani (notice how the crazy increases with the list)
D. Hunter (my candidate for Next Serial Retread)
Don't forget Hilary and possibly Al Gore. Those two together as pres./VP would kick Obama's ass.