411.com
411.com offers white and yellow page lookups, area and zip code lookups, and reverse searches for phone numbers addresses.
http://www.411.com/

Anywho
Anywho provides nationwide telephone directory listings, area code look-ups, reverse searches from phone numbers to the owners, and a toll-free number search.
http://www.anywho.com

Escape Artist
Escape Artist provides dialing codes for calling other countries, directory service, links to embassies, conversion services, maps, and electrical voltage for travelers.
http://www.escapeartist.com/global/telephone.htm

gethuman
gethuman offers hope to people who dont want to deal with phone trees when trying to contact customer services at companies nationwide. gethuman lists companies and methods for circumventing their phone trees.
http://www.gethuman.com

Infobel.com
Infobel offers links to telephone directory services worldwide.
http://www.infobel.com/teldir/

Internet 800 Directory
Internet 800 Directory searches for toll-free numbers nationwide.
http://www.inter800.com

PeopleFinder
PeopleFinder offers free searches for telephone numbers and addresses including reverse searches.
http://www.peoplefinder.com/

PhoneNumber.com
PhoneNumber.com offers searching for phone numbers, area codes and zip codes, and reverse searches by address and phone number.
http://www.phonenumber.com/

Postal Codes for Other Countries
EmbassyWorld provides postal codes for other countries.
http://www.embassyworld.com/data/Zip_Codes.html

Switchboard
Switchboard.com provides access to telephone directory listings.
http://www.switchboard.com

Zabasearch
Try Zabasearch for telephone and address searches.
http://www.zabasearch.com/

Zip Code Search
The United States Postal Service offers this Zip Code search service.
http://www.usps.com/zip4