Following are a couple of informative links describing the makeup of the electorate:
Pew Research Electorate Demographics
Gallup Polls Electorate Demographics
The Pew survey is a year old, but it’s the latest one they’ve published as far as I can tell. As a matter of fact, it looks like the publication of data for last year is at least a couple of weeks late. Anyway, I doubt there’ll be any kind of major sea change in one year’s time. It also enjoys the major advantage of a large sample size. (Table of measurement errors on page 2.)
The Gallup survey is newer (January) but doesn’t go as in-depth. I’m sure the full data set is available somewhere on their site, but I haven’t gotten into it yet.
This stuff has probably been posted here before, but I think it should be required reading for anyone interested in electoral politics. Besides, I’m an unoriginal bastard.
The only major limitation is that they don’t treat income level.