For the top four US presidential candidates from each party, InTrade.com gives these chances of nomination, becoming president, and the implied conditional chance of winning if nominated:

Al Gore’s conditional chances seem way out of line to me.  And Ron Paul’s conditional chances are suspiciously large compared to the other Republicans.

Added: What good are estimates that could be better?  I know of no other source of daily-updated estimates with even a similar accuracy.  And here anyone can be paid to fix any errors they find.