Mine: I mostly agree with (read: plagiarized) Kandahar.
Republicans, I think, will see a deepened civil war between the Conservatives and the Moderates. Romney will be blamed (similar to how Democrats turned on Kerry) as an awkward, flawed candidate whom few were excited about except as an alternative to the guy in place. Conservatives will draw a straight line from the Reagan / Bush II victories through the H.W / McCain / Romney losses and claim that those who strongly embody conservative concepts (I know, that claim is questionable about W, but in 2004 few doubted his credentials) succeed by making the case for conservatism, while those who do not fail by painting in pastels and representing a weaker Democrat vision. This fight would be brutal in the short term, and make the party better in the long term; forcing Republicans to continue to be the Party of Ideas through sheer bloody competition. Republicans would be well-situated to repeat the Democrat trick of 2006/2008 wherein they expand their congressional holdings in 2014 and then pick up the Presidency in a second wave-election in 2016. This only works, however, if the 2016 candidate is acceptable to Conservatives as one of their own - a "hold your nose and vote" argument is unlikely to work for what they will see as the third time in a row. If the party nomination in 2016 is a McCain/Romney type, look for lots of Conservatives to either sit out the race, or vote third party. Whether those numbers would be enough to counteract the exhaustion with the Obama administration on the part of the public is a matter I would say is too up in the air at this point.
Democrats are generally much more confident in their victory than the situation seems to warrant. They will therefore blame insidious outside forces for their loss. Instead of turning to infighting, Democrats will blame a combination of 1. George Bush, 2. Election fraud, and 3. Citizens United. Despite the money advantage enjoyed through much of this race by their party (and its' affiliates), they will draw for their more simplistic voters a simple narrative of "Romney is rich, therefore he bought the election, and where he couldn't buy votes, he bought the vote-counters." They will be MUCH more acrimonious in their response to a Republican administration in this instance than Republicans will be towards a second Obama administration, as they will be have developed a narrative that President Romney is illegitimate. Much of the Bush-hyperbole that we saw began with the same impression, so expect to see rabid assaults on the Romney administration as soon as he begins to make good on any basic campaign promises. Absent a second recession, Democrats will be less suited to dramatically expand their Congressional seats in 2014 than the Republicans would, and it is not inconceivable that there will be a push for Obama to run again in 2016, perhaps leading to the fun (for conservatives) show of another Obama-Hillary face-off
. In such a case, look for Hillary to win (the 'stolen election' narrative will have lost some of it's pull for Democrats by that point, being superseded by anger at the particulars of the evil Romney administration); Obama made himself few strong allies in the Party over the last four years, and Hillary will be able to speak with authority on his administration, having served in it.