Directories

People

Anywho: Telephone Directory with Reverse Lookup
Infobel (Telephone Directories on the web)

Businesses

Airline Toll-Free Numbers and Websites
Infobel (Telephone Directories on the Web)

Geographic Codes

International Calling Codes
Internet Country Codes
National Address Server: Adds zip+4 to valid US postal addresses and can print them for labels.
USPS Zip Code Lookup

Government

Congressional Email Directory: Finds email addresses of senators and congressmen.
Federal Web Locator: For finding federal government information.
FedWorld Information Network: For locating government information.