Whois is a service that allows the public to look up domain name registration information (Wikipedia has a great article).

The following services allow free public whois lookup:

1. Alexa.com | external link
2. DomainTools.com | external link
3. SamSpade.org | external link
4. WhoisFinder.com | external link
5. Whois.bw.org | external link
6. BetterWhois.com | external link
7. IWhois.com | external link
8. Whois.com | external link
9. Whois.net | external link
10. Whois.sc | external link <- Now DomainTools.com
11. DnsStuff.com | external link
12. Whoistag.com | external link
13. Registro.br | external link
14. OneWhois.com | external link
15. ...add more here