WhoisThisDomain - Domain name lookup tool that allows you to get information about domain registration from WHOIS server.
ViewDNS.info - Free DNS related tools including Reverse IP Lookup, DNS Propagation Checker, Chinese Firewall Test...
Active Whois Browser - Browse all information for an IP address or domain name with a single click!
Whats My DNS - Instantly check your domain names current IP address and DNS record information against multiple name servers located in different parts of the world.
DomainTools - Domain name research, including comprehensive Whois Lookup, Reverse Whois Lookup and Whois History.
Domain Details - Displays Server Type, Headers, IP Address, Location Flag, and links to Whois Reports.