Blue indicates counties that voted more Democratic than in 2004. Red indicates counties that voted more Republican than in 2004. The darker the color, the greater the change.
Click map for larger version.
From an interactive feature at The New York Times: How the Map Changed From 2004.
It looks like Indiana was the biggest swing state. It swung the most toward the Democratic Party. There was a lot of ticket-splitting due to a relatively very weak Democratic candidate for governor (Jill Long Thompson) against incumbent Mitch Daniels.