Mail Addresses

National Address Server - from SUNY Buffalo
MelissaData - Look up U.S. addresses and get ZIP+4 code, area code, more. Also has lists of ZIP codes by county, reverse lookups, etc.
U.S. Postal Service ZIP Code Lookup

Telephone Numbers

AnyWho - AT&T's directory; do reverse lookups, ask for street proximity listings, and get maps of an address.
CSU Monterey Bay Faculty-Staff Directory
Switchboard - Residential and business telephone numbers and yellow pages.
Infobel - Index of world phone books, including individual and multiple country directories.
WhoWhere - Residential and yellow pages; can be searched in English, French or Spanish.

E-mail Addresses
Free Email Address Directory - Listing and review of free email providers
Topica, the Mailing List Directory

Reverse Directories

AnyWho - Reverse telephone directory; enter phone number
Switchboard - Reverse phone and address directory