ViewDNS.info - Free DNS related tools including Reverse IP Lookup, DNS Propagation Checker, Chinese Firewall Test...
DomainTools - Domain name research, including comprehensive Whois Lookup, Reverse Whois Lookup and Whois History.
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.
APISpot.io - Bulk WHOIS and Domain Names API on steroids, Parsed and in JSON, Domain Availability Check, Domain and WHOIS Lookup
CubDomain - CubDomain.com is the site to check website's statistics, Information, Whois Record, Hosting...
DNSdumpster.com - Open source domain intelligence lookups for security recon