United States Postal Service Site
http://www.usps.gov

Rate Information and Other Services
http://www.usps.com/rates/extra-services-rates.htm

International Mail
http://www.usps.com/international/sendmail.htm

Domestic Mail
http://pe.usps.com/text/dmm100/intro.htm

ZIP Code Look Up
http://zip4.usps.com/zip4/welcome.jsp