http://www.four11.com/Sled.html
The Four11 Online User Directory is a directory of online users and their e-mail addresses, with almost half a million listings. It allows you to search by any combination of first name, last name, location, old e-mail address, and current or past organizations. An optional paid membership provides additional services, including an expanded list, search agents, links to a Web page, and PGP key services.