I'd still like to see what else the Democrats have to offer besides Hillary.
A list here hits some of the significant ones.I'm not sure about Biden running. I don't see his odds as all that good and there's not really much more to gain for him. He turns 74 in November '16, which is not attractive even for another term as VP. He would also be running hard on Obama's record, which is always an awkward position. Sitting VPs don't have the best history when it comes to upgrading.
Pretty sure that Martin O’Malley is running even if it's hopeless. He's been acting like he's gearing up for a while now, and is term limited. If he wants to move up then he needs the national profile that a primary run (even losing to a Clinton coronation) would help build. 2016 would likely just be a setup for 2020 after a Romney style extended campaign.
Elizabeth Warren and Kirsten Gillibrand are both rather attractive ideas to run against Hillary, as they are considerably more liberal than her and remove the Clinton baggage while still being, well, women.
Warren polls third behind Biden and Clinton, but is very close or ahead of Biden in some
Iowa and
New Hampshire polls. Such numbers are completely meaningless this far out, but if she could get a strong showing in one of the early votes she could draw considerable numbers of voters away from Clinton.
Another name I've seen;
Julián Castro is probably too young and inexperienced (three term mayor of San Antonio, previously city councillor, soon to be HUD secretary) but has been promoted hard by the party and discussed as either a VP candidate or future national prospect. His
twin brother already holds the obvious House seat and there is no Senate seat available (and a win in Texas might not be likely anyway), so a primary run might be his best bet to keep moving forwards.