Alabama

[mileslunn]

My guess is one could use a racial breakdown map and it would probably be pretty close to the actual results.  Mississipp, Louisiana, and Alabama strike me as the most racially polarized states.  In Alabama, 9 times out of 10 you could guess right how someone voted just by looking at their skin colour.  I also don't think this just has to do with Obama being Black as I believe Bush got around 85% in 2004 amongst Alabama whites, while Kerry got between 90-95% of Alabama Blacks.  Now true Blacks vote heavily Democrat regardless of location whereas the white population is far more evenly split and there are some sections such as New England, West Coast, parts of the Upper Midwest where the white population generally favours the Democrats by margins outside of the statiscal margin of error (in the Mid-Atlantic, most states were within the statistical margin of error amongst whites in the 2008 election).  Even in other southern states, such as Arkansas, North Carolina, and Tennessee, the Democrats still almost always get over 30% of the white vote. 

[mileslunn]

Mississippi is even more racially polarized than Alabama, FWIW.

I would say Alabama is probably the second most racially polarized state, although I agree Mississippi is the most racially polarized.  Here are the Mississippi results according to the CNN exit polls

2004

85% of Whites voted for Bush
94% of Blacks voted for Kerry

2008

88% of Whites voted of McCain
98% of Blacks voted for Obama