Bulk Whois API - Bulk Whois API is a provider of parsed WHOIS data in JSON with simple API, competitive pricing, top notch support, and more.
CubDomain - CubDomain.com is the site to check website's statistics, Information, Whois Record, Hosting...
Whoisology - Connected database of whois records and whois history
Website Informer - Website.informer: complete data lookup & free aggregated report on any domain including whois, visitors, IP & DNS details, competitors, owners, etc
WhoisThisDomain - Domain name lookup tool that allows you to get information about domain registration from WHOIS server.
DomainTools - Domain name research, including comprehensive Whois Lookup, Reverse Whois Lookup and Whois History.