The maps posted thus far are misleading because -- due to American elections being 'winner take all' -- a district that is "for" Obama may have had plenty of Romney votes but will still register as blue, and vice versa. This obviously applies to whole states that register as red or blue for the electoral college as well, painting a false picture of 'red states vs blue states'. The reality is that we are a big purple blob:
But even the purple blob obscures things somewhat because it doesn't differentiate between levels of partisanship, i.e., moderates vs extremists. This is how voters self-identity:
So in both red and blue states most* voters are centrists. Don't let the extreme partisanship of the political class (the media, politicians, activists) fool you into thinking the whole nation is that way!
*In the sense of "the largest share"