Whoisology - Connected database of whois records and whois history
Active Whois Browser - Browse all information for an IP address or domain name with a single click!
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.
DomainTools - Domain name research, including comprehensive Whois Lookup, Reverse Whois Lookup and Whois History.
WhoisAPI - WhoisAPI is the premier provider of freshly parsed whois data for domain names and IP addresses...
ICANN WHOIS - The official ICANN WHOIS search for domain lookups.