I had reason to look up the US Postal Service web site this week (http://www.usps.com) and I thought I would report in on some of the features:
Zip look up: http://zip4.usps.com/zip4/welcome.jsp
OK I’ve been using this for years. Type in an address and they’ll give you the zip code
Mail Forwarding: http://www.usps.com/receive/choicesfordelivery/receivemailinotherplaces.htm
You can request online to have your mail forwarded if you have a credit card with the new address but I also found out that you can have your mail forwarded anywhere even overseas. It costs $1 to do this online, but it’s free if you do it in person.
Keep in touch: http://www.usps.com/netpost/stayintouch.htm
You can place an online order for a real letter or postcard to be sent to a given address.
You can learn all about the history of the mail.