The South doesn't want to secede from the Union, despite what some people usually think.
I don't think they do either, and they probably won't within 100 years, but if I had to pick a most-likely-to-secede, it would be the ex-Confederacy.
@SalmonGod: Huh? As in, we're a third world country but there's a small population of obscenely wealthy people? Or as in, we're a third world country but most of the population is comparatively obscenely wealthy? Because our poor people ARE obscenely wealthy by world standards, but I'm not sure where the third world country comes in.