Whoisology - Connected database of whois records and whois history
Domain Details - Displays Server Type, Headers, IP Address, Location Flag, and links to Whois Reports.
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.
ViewDNS.info - Free DNS related tools including Reverse IP Lookup, DNS Propagation Checker, Chinese Firewall Test...
WhoisAPI - WhoisAPI is the premier provider of freshly parsed whois data for domain names and IP addresses...
Whats My DNS - Instantly check your domain names current IP address and DNS record information against multiple name servers located in different parts of the world.