General Directories

AnyWho - from AT&T,  Area Codes, White and yellow pages, international directories, reverse lookups, and toll-free searches.

Switchboard - from InfoSpace, nationwide residential and business directory

WhoWhere - from Lycos, white and yellow pages

People Search - from Yahoo, search for phone numbers and email addresses.

Specialized

Internet 800 Directory - from DIANCO, search by product or service, company name, or toll-free number.

ZIP Code Lookup - from the United States Postal Service, find the correct ZIP+4 for any address or company or find a list of cities by ZIP code