Former presidential candidate and one-time hype man Howard Dean is not necessarily out of the question for 2016.
From an Associated Press report on the "fresh start" Hillary Clinton will need with Democratic voters:
Former Vermont Gov. Howard Dean, who sought the party's presidential nomination in 2004, said he expected Hillary Clinton to face a primary challenge. But Dean predicted she would "satisfy a large number of Democratic voters, including a large number of progressives." ...
Asked whether he was considering another run, Dean was blunt: "Nope. Not as long as Hillary's in."
Clinton, for her part, has maintained that she has not yet decided whether she will run.