It's not entirely unusual to start jockeying for the White House only days after the election, and this time was no exception. Of course, four years is a long time, and the names that were batted around in 2008 and 2004 and 2000 ended up not meaning a whole lot, so don't take too much stock in what's being talked about now. Still, why not do some baseless speculation?
For the Republicans, they benefit from having a huge pool of politicians. The winners in 2010 and even 2008 have now gained enough experience and political capital to be contenders, and the disaster of the Romney campaign has flushed a lot of the old guard out. Still, the names that keep resurfacing for the GOP--namely, Marco Rubio, Bobby Jindall, and Chris Christie--bode well for those looking for change in the GOP. Christie and Jindall predate the Tea Party movement, and while Rubio has certainly benefited from their support he never properly signed on to the movement. While they all hold traditional Republican positions, there's enough diversity in their political pedigree (Christie is a moderate, while Jindall has had years of hands-on management of a disaster-ridden state) to be actively different. Rubio is still early in his senate career, so there's plenty of opportunity for growth (and disaster, of course), but the demographics (Florida + Hispanic) suit him perfectly.
I'll throw my own names in there, namely Nikki Haley and Kelly Ayotte. Haley is the Governor of South Carolina, and a decent if unremarkable choice. She still has some proving to do during her tenure, which has been quiet and lackluster so far. Ayotte, a current Senator from New Hampshire, is a solid, moderate Republican but has little name recognition. Aside from that, very few of the candidates--potential or otherwise--from the last election will appeal to many next election cycle, with the exception of Jon Huntsman, Tim Pawlenty, or John Thune. All are solid, uncontroversial conservatives (and, in Huntsman's case, appealingly moderate). Anyone else that will probably run, such as Rick Perry, Rick Santorum, or Paul Ryan, will probably be successful; if none of the new upstarts are unable to get a quick foothold these stalwarts will be an early favorite.
The wild card for the Republicans is going to be Rand Paul. He clearly has presidential aspirations, and he's a clear beneficiary of the Tea Party. And yet he doesn't quite fit the conservative template. His position on gay marriage is the same as Obama's (he wants to let the states decide) and he routinely is the voice of opposition for defense spending and the drug war, both cause celebres of conservatives. He also holds many positions much more libertarian than conservative. However, many of his other positions--which he would call "nuanced" but everyone else calls "controversial"--probably will mean he has no political future. (For example, his position on private property trumping the Civil Rights Act of 1964 sounds reasonable in an academic sense, but it will take a rival politician seconds to simply call him--with some political justification--a racist.)
The Democrats are a little less interesting; most likely Biden will run (and probably win); if he chooses not to, for whatever reason, Hillary Clinton will instead. (It's always possible, of course, that Hillary runs regardless.) Both are moderate Democrats, but both are probably too old to run in 2020 so there may be some keen competition between the two. There is a pretty good chance that a young upstart will also run--even if they lose, they'll force the party more to the left and will easily make a name for themselves. That person probably hasn't seen their political fortunes rise just yet, although Julian Castro (mayor of San Antonio), Cory Booker (mayor of Newark), and Elizabeth Warren (Senator-elect of Massachusetts) are good potential candidates. However, none have been around long enough (or a high enough office) to really make a proper impact.
Obviously, everything will change in four years, so don't follow things too terribly closely. Still, place your bets now.