I'm usually not a big fan of George Will (who is?), but he actually has a pretty good article in the Washington Post arguing that most people misunderstand some of the reasons why the South is now a Republican stronghold.
The crux of his argument is that the South is no longer the poverty stricken region dependant on government subsidies that it was 50 years ago, and that the most heavily Republican districts in the South are not in rural areas but are in rapidly growing suburban districts. As someone from suburban Atlanta, one of the fastest growing and wealthiest areas of the country, I can absolutely vouch for this. The Democrats would win every single election in Georgia if it wasn't for two or three very well educated and affluent counties surrounding Atlanta.
I will admit though that Will downplays the importance of both the civil rights movement and today's hot button social issues, but the argument is still largely accurate. Check it out.
http://www.washingtonpost.com/wp-dyn/articles/A14294-2004Feb4.html