If you’re interested in American dialect words, look no further than the Dictionary of American Regional English (DARE). The nearly completed multi-volume dictionary (with Volume I, A–C released in 1985 and Volume V, Slab–Z due in 2011 [Fall 2010 newsletter]) would cost you hundreds of U.S. dollars (electronic version coming eventually), but on the site you can get 100 sample entries, plus quizzes and more.
You can also get a word a day by following darewords on Twitter. I have.