WhoIs Resource for Domains
WhoIs information provides a glimpse into who owns the current
registration for a domain. Not all domains can be
searched, some are protected in many different manners.
Should you require information on a domain whose information is
protected, you might try emailing the owner at either webmaster
or postmaster @ the domain's address. They may or may not
answer you, but you can try if it is necessary to contact a
domain owner.
Some Good WhoIs Sources
Network Solutions - These guys are a great resource for domains and information.
Sam Spade - Sam Spade is a great tool, many times it will give results when others have failed.
Domain Query - This is another awesome tool. You can perform a great deal of searches including IP WhoIs and DNS searches.