According to Judicial Watch:
6. Governor Mike Huckabee (R-AR): Governor Huckabee enjoyed a meteoric rise in the polls in December 2007, which prompted a more thorough review of his ethics record. According to The Associated Press: “[Huckabee’s] career has also been colored by 14 ethics complaints and a volley of questions about his integrity, ranging from his management of campaign cash to his use of a nonprofit organization to subsidize his income to his destruction of state computer files on his way out of the governor’s office.” And what was Governor Huckabee’s response to these ethics allegations? Rather than cooperating with investigators, Huckabee sued the state ethics commission twice and attempted to shut the ethics process down.
Other presidential candidates on the list include Hillary Clinton, Rudy Giuliani and Barack Obama.
Although not on the list, John McCain seems to have a dark side too.