Addresses.com
The largest e-mail address database and directory on the web. Varied method of performing searches using phone numbers, e-mail and home addresses. Also able to search for businesses, zip codes, area codes, schools and even persons.

AnyWho Find People
An easy search form for phone, address, or E-mail. Does a "begins with" search that others won't.

Bigfoot
Claims to have the largest database of E-mail addresses.

Congressional E-mail Directory
E-mail for the U.S. Congress. Pick a state, or searchable by name.

Emailaddresses.com
A guide to finding E-mail addresses.

Finger
An old-style Unix tool for finding out a little bit about people, if you have their E-mail addresses. You can still "finger" some accounts, and read the information file, using the finger tool. This site is a Web interface to finger.

High School Alumni
Allows high school alumni to list themselves, not a free service.

http://infospace.com/reverse.htm
In case you know the E-mail address and not the name.

Infobel
Now part of InfoSpace.

InfoSpace E-Mail Addresses
Also quick. See also InfoSpace's reverse directory.

Internet Address Finder
Includes a reverse directory for phone and E-mail. Allows wildcards.

MESA
Claims to be "the largest E-mail address book worldwide."

PeopleSearch.net
Includes a reverse search by phone number, E-mail, address.

Switchboard E-mail search
Another straightforward search.

Usenet Addresses Database
Search for E-mail addresses if you know the name of the person, or the name of their organization. Addresses are collected from Usenet postings, so you'll find only people who have, um, posted to Usenet.

WHOIS
Maybe you can find a person or organization by searching for its Web domain names, such as creator.org or elvisisalive.com. Listings include name, address and E-mail address. Search in the registry of top-level domains (only .com, org., .net). Use just the domain name (yahoo.com), not a full URL (www.yahoo.com or http://www.yahoo.com). Note the help file for other options, including searching by company name.

WhoWhere?
Another E-mail search. No reverse lookup.

World Email Directory
Worldwide email databases. Search by name, city, country or business. Want to be found? Add your information.

Yahoo people search
A quick search for E-mail. Was four11.com. No reverse lookup.