WhoisAPI - WhoisAPI is the premier provider of freshly parsed whois data for domain names and IP addresses...
WebCargo - Optimize your workflow by offloading it to us. Useful API's with seamless integration that scale to your needs.
ICANN WHOIS - The official ICANN WHOIS search for domain lookups.
DomainTools - Domain name research, including comprehensive Whois Lookup, Reverse Whois Lookup and Whois History.
WhoisThisDomain - Domain name lookup tool that allows you to get information about domain registration from WHOIS server.
DNSdumpster.com - Open source domain intelligence lookups for security recon