MxToolBox - All of your MX record, DNS, blacklist and SMTP diagnostics in one integrated tool.
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.
intoDNS - IntoDNS checks the health and configuration and provides DNS report and mail servers report.
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.
Dnsstuff - DNSstuff offers DNS tools, Network tools, Email tools, DNS reporting and IP information gathering.
NsLookup.io - A simple and powerful tool for querying DNS records