United States Postal Service: Zip Code Lookup - Find the postal code for a United States address.

Postage rates worldwide - Directory of mail rates (domestic & international letter rates) with links to the rate calculators or rate tables of postal services in most countries of the world. email rate queries supported.

Jay Computer Services Zip Code and Area Code Lookup - Zip codes, cities, states, counties, area codes, and time zones. Do zip code proximity calculations. Extensive area code change information.

National Address and ZIP+4 Browser - Interactively browse all address and ZIP+4 records in the United States.

SpeedKeys.com - SpeedKeys is a fast and easy zip code, city, state and area code look-up program. It can also generate an optional PostNET Barcode.

Census Bureau Place and Zipcode files - A by-product of map-work done by the US Census Bureau. Access zip codes by longitude, latitude, and city name.

ZIP Code Lookup - Lets you get a list of all ZIP codes in a city, county, or area code.

International Mailing Address Formats - Includes format information and/or examples for many countries, and links to additional references.

DirectMailQuotes LLC - Zip code directory lookup as well as postal rates, regulations, glossary of mailing terms.

ZIPFind's Postal Code Calculator and Data - Calculate distance in miles between two ZIP Codes. Find all ZIP Codes within a radius of a ZIP Code.

Free ZIP Code Lookup - Free zipcode lookup with areacode, county, latitude, longitude, MSA, PMSA, congressional district, FIPS code, and timezone. Updated monthly.

Canada Post: Postal Code Lookup - Look up postal codes for any address in Canada. Also look up address ranges for given postal codes.

The National Address Server - "Given a valid U.S. postal address, this server attempts to rewrite the address in the proper format along with the ZIP+4 code."