As I and innumerable others have mentioned, the red states that seem genuinely ripe for flipping this year are Colorado and Virginia. Others are definitely possible. But those are the ones that might even be considered probable.
The most recent poll of Viriginia
(May 22nd) has Obama beating McCain by 7 points (49%-42%). And the one immediately previous has Obama down by 3 points (47%-44%).
Colorado is even stronger for Obama. The most recent poll
(Rasmussen, May 21st) has Obama up by 6 points and the one previous to that (Ramussen, April 21st) had him up by 3.
TPM Reader DS
sent me to this electoral college widget
and fiddling around I found that if I gave the Dems Virginia and Colorado, I could get them to victory while losing Florida, Ohio, North Carolina, Missouri, New Mexico and Nevada. The other states I'm giving the Dems all seem eminently winnable, though a few in the upper midwest will certainly take some hard work.
Of course, there are a million different ways to divide up the electoral votes. But since I'm increasingly confident that Obama can actually win Ohio, this put me in a bullish state of mind.