A poster on Mudflats has looked at all the first term Governors in the USA since 1900 - all 1200 of them. They found that there have been only three who have resigned without being forced to do so:
Jim McGreevy, Eliot Spitzer and Sarah Palin.
Jim McGreevy "coupled the announcement of his decision to resign with a public declaration of his homosexuality and an admission to having had an extramarital affair with the man he had appointed homeland security adviser".
Eliot Spitzer was alleged to have been involved in a prostitution ring.
Sarah Palin resigned because.....um.............er....................ah yes, she didn't want to be a lame duck.