Dnsstuff - DNSstuff offers DNS tools, Network tools, Email tools, DNS reporting and IP information gathering.
Brandpa - Domain names for startups
MxToolBox - All of your MX record, DNS, blacklist and SMTP diagnostics in one integrated tool.
Nuage - Nuage provides domain naming services.
SolveDNS - SolveDNS works to check your name servers, a records, and mail servers, SOA records for errors, consistency, efficiency and speed using several DNS tests.
Tool.Domains - Search free to register expired domains