FiveThirtyEight.com has an interesting post comparing the 2008 electoral map with the 1992 electoral map. Which states voted more Democratic last week as compared with when Clinton won his first term? Which states voted more Republican?
Basically the Republicans have made notable gains in the western Appalachian states, the Mid-South, the southern plains, and the mountain west. Meanwhile, the Democrats have solidified their hold on the Northeast, while making gains in the Midwest, Pacific coast, and southern Rocky Mountains.
The summary:
Essentially, by sacrificing 50 or so Electoral Votes from the inland South, the Democrats have taken about 60 votes from former swing states and turned them into Lean Democratic states, and another 44 or so from former lean Republican states and turned them into swing states. This is a good trade-off.
See the post for a map and full Electoral College breakdown.