Here are more links on salestax-usetax.com
Wikipedia includes several articles on sales and use taxes including a general article on sales taxwhich is not specific to the US. Then, there's an article on sales taxes in the United States which is includes a capsule summary of each state. Don't expect much from the summaries. Some states have lots of detail, and some states have a sentence or two. There's also an article on use tax.
Sales Tax Guy