Of all the red/blue voting maps...

...I think this one is perhaps the most interesting. It shows not the majority choice (blue=Democrat, red=Republican), but the change since the 2004 election. Dark colors are 15% or more shifts toward that party, light colors lesser degrees of shift.

At the primary link [click on "voting shifts"] you can zoom in to go county by county to see how preferences have changed, and can examine the change since other elections in 2000, 1996, and 1992.