ViewDNS.info - Free DNS related tools including Reverse IP Lookup, DNS Propagation Checker, Chinese Firewall Test...
WhoAPI - WhoAPI is an API service for mass requests of domain information like domain registration availability and structured whois data in JSON.
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.
WhoisThisDomain - Domain name lookup tool that allows you to get information about domain registration from WHOIS server.
Domain Details - Displays Server Type, Headers, IP Address, Location Flag, and links to Whois Reports.
Complete API - All the APIs you need under one roof: SMS, Geolocation, Whois and Currency APIs now available!