Travel in the U.S.
Taxes in the U.S.
This document should be helpful. It is a brief submitted by the Federation of Tax Administrators to the President's Advisory Panel on Tax Reform in April 2005, and is a very useful summary of the policies of the various states towards sales taxes, the bases on which they grant exemptions, and the prevailing rates of taxation. http://www.taxreformpanel.gov/meetings/pdf/Salestax_04182005.pdf
Other testimonies submitted to the Advisory Panel at:
http://www.taxreformpanel.gov/ may also be useful. You can register to receive e-mail updates as new testimonies etc. become available