The Whois system was designed to let people find out who owns a particular domain. This Whois information is public information unless a domain owner has a special privacy service from their registrar. There are many Whois services which offer free Whois lookups. Wikipedia has a great article about Whois here.
- ICANN.org (official ICANN site)
- ICANNwiki.org (independent wiki)
- DomainTools.com (popular Whois service)
- Alexa.com (traffic rankings and Whois information)