There is now an April 2011 version of IRS Publication 901, U.S. Tax Treaties, on the IRS website. The publication was last revised in April 2010. It includes information on whether a tax treaty between the U.S. and another country offers a reduced rate of, or possibly a complete exemption from, U.S. income tax for residents of that particular country. In the back of the publication there are tables that show: (1) the countries that have income tax treaties with the U.S. (Table 3); (2) the tax rates on different kinds of income (Table 1); and (3) the kinds of income that are exempt from tax (Table 2). The list of tax treaties in Table 3 has been updated through March 31, 2011.
The “What's New” section of IRS Publication 901 notes that the U.S. has exchanged instruments of ratification for a new income tax treaty with Malta and a new protocol amending the income tax treaty with New Zealand. The provisions for withholding tax at source in both of the above documents are effective for amounts paid or credited after Dec. 31, 2010.
The IRS says that Publication 901 should only be used as a quick reference guide, as it is not a complete guide for all provisions in every income tax treaty.