I'd say that the US has about 8 distinct genres of accent: far North-East, Boston, New York City, ghetto, Wisconsin, Midwest, mild Kentucky twang and deep South.

JazzO, I figure you're joking, but at the risk of YARTing, may I respectfully direct you to the late, great Frederic Cassidy's Dictionary of American Regional English and its little sister, the Linguistic Atlases:

http://polyglot.lss.wisc.edu/dare/dare.html