WhoisThisDomain - Domain name lookup tool that allows you to get information about domain registration from WHOIS server.
DomainIndex.com WHOIS Database Download - Get domain price, keywords, searches, ngrams | Domainindex.com
Whoisology - Connected database of whois records and whois history
IQWhois - IQWhois provides a comprehensive & customized WHOIS database download with over 300 million domains & 3000 TLD's for domain name WHOIS registration information.
JSON WHOIS API - Parsed domain WHOIS data from any WHOIS server via RESTful API with metered pay as you pricing.
Domains Index WHOIS Database Download - Domainers can scout for new domain names and business opportunities without breaking the bank with the help of Domain Index’s WHOIS Database Download.