The full list of U.S. postal abbreviations are posted on the Internet by the U.S. Postal Service at (www.usps.gov/ncsc/lookups/usps_abbreviations.htm).
In addition, the two-letter postal abbreviations for the 50 states are listed in the World Almanac, the front of the National Zip Code Directory, The New York Public Library Reference Guide and probably many other places. You can also get the abbreviation for any particular state by looking at the addresses in most geographically organized directories (e.g., the AALL Directory & Handbook or the State Yellow Book).