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.
Domainr - Domainr is the only ICANN-accredited domain status API provider.
DNSChecker.org - Check DNS Propagation worldwide. DNS Checker provides name server propagation check instantly. Changed nameservers so do a DNS lookup and check if DNS and nameservers have propagated.
Instant Domain Search - Search domain names instantly by showing results as you type.
NsLookup.io - A simple and powerful tool for querying DNS records
Lean Domain Search - Find a Great Domain Name w/ twitter handle availability