Is there any way to lookup a domain's registrar?

You can lookup the registrar using whois.

For example, you can go to http://www.network-tools.com/, type in the domain, select to view whois information, and you will see the domain's registrar.

Peter

For CNO domains, the definititive answer is always at http://www.internic.net.

-t

Try this http://www.verisign-grs.com/cgi-bin/whois