Whoisology - Connected database of whois records and whois history
DomainTools - Domain name research, including comprehensive Whois Lookup, Reverse Whois Lookup and Whois History.
WebCargo - Optimize your workflow by offloading it to us. Useful API's with seamless integration that scale to your needs.
APISpot.io - Bulk WHOIS and Domain Names API on steroids, Parsed and in JSON, Domain Availability Check, Domain and WHOIS Lookup
WhoisThisDomain - Domain name lookup tool that allows you to get information about domain registration from WHOIS server.
Domain Details - Displays Server Type, Headers, IP Address, Location Flag, and links to Whois Reports.