ARIN WHOIS Database Search This database contains IP addresses, autonomous system (AS) numbers, organizations or customers that are registered with ARIN.
Sam Spade It takes a hostname or an IP address, guesses at the domain name, and then runs some whois queries to find out who owns the domain and the block of IP addresses it lives in, and traces the route packets take to the host.
Usenet-Addresses (MIT) This service allows you to search for e-mail addresses if you know the name of a person, or the name of the organization that provides their net access.