Hillary seems to be the only heavyweight name in the mix, but I honestly don't think she wins it. Historically, it is rare for the same party to keep office in a non-incumbent year. It happens if the predessor was wildly popular (i.e. Reagan giving way to Bush 41), but otherwise it doesn't happen. The only other time in the past century when the same party retained power was Herbert Hoover being elected after Calvin Coolidge, and then we got the Great Depression amiright? Truman and LBJ retained the party's power after their predecessors, but they took over after the deaths of FDR and JFK and essentially got to run as incumbents by the time the election rolled around.
Obama is not a popular president. Unless he gets a wild surge in his last couple of years, I have a hard time seeing a Democrat getting elected, even with Hillary's stardom and the lack of competent Republicans.
On top of that, I think Hillary brings to much baggage. I am pretty liberal by the way and rather like Hillary, but she has always been a polarizing figure, and I'm not sure if she'd be able to pull enough of the middle voters to the left coming off of Obama's low approval rating. If Hillary was the candidate, the campaign would be brutal as the 'Pubs would dredge up Whitewater, Vince Foster, Monica Lewinsky, and all of those images of her looking fat and disheveled that the right wing has been joking about for years. The Republicans have been bracing for a Hillary Clinton campaign for two decades. It would be ugly. McCain got blasted for his age during the 2008 race. Hillary is only a couple years younger, so that could be a possible issue as well.
Not only that, but there is something to be said about moving forward instead of trying to go back in time. I thought Clinton was a pretty good president, but the 90s were a long time ago and getting further away every day. For the same reason, I don't think the country would have the stomach for Jeb Bush, simply because of his name. This country needs to move on from the Bushes and Clintons.
The Republicans haven't really put out anyone qualified or sane in the last couple of years to make a name for himself and unify the party, let alone the country. But I would bet we see some shiny new faces after the 2014 elections to gear up for the election. They will probably find their own version of Obama (which they have been trying to do for years already) and forget about all of the "community organizer" and "executive experience" rhetoric they tried a few years back. But even if they can't find Mr. Right for 2016, I bet they find a Mr. Right Now who is clean enough to take the election, because I don't think the Democrats will have enough national strength to carry it again.