Clothing, footwear, and school supplies will be tax-exempt (some restrictions apply):
Florida: July 24th - August 1st
Texas: August 6th - 8th
Georgia: July 29th - August 1st
New York: August 25th (only in Montgomery County and Johnstown)
Those are all I could find right now. If you find any other state tax-free info., just post here. Thanks!