WhoisThisDomain - Domain name lookup tool that allows you to get information about domain registration from WHOIS server.
WebCargo - Optimize your workflow by offloading it to us. Useful API's with seamless integration that scale to your needs.
Whoisology - Connected database of whois records and whois history
JSON WHOIS API - Parsed domain WHOIS data from any WHOIS server via RESTful API with metered pay as you pricing.
JsonWhois.io - JsonWhois is the leading cloud hosted Whois API.
ICANN WHOIS - The official ICANN WHOIS search for domain lookups.