US Sales tax rates (all States).
While this will help any/all types of business, it will be of tremendous use for online business in the collection and remittance of sales taxes.
Ideally data should be provided by State agencies as a public service (official/accurate rates). It is in their best interest to provide this information to assist in their tax revenue and provide essential/local services - the cycle benefits everyone.
Its a wonder that this isn't already done (by State governments). The debate over internet sales tax is hampered by the real complexity of taxes across State borders.
Providing this information without the cost burden (of paying for private services that do the same thing) will help ease/remove that difficulty, and finally help our own communities economically.