Domain Tools – offers a large selection of tools to test the domain name server. This is helpful if you are trying to use custom domain mapping for blogger
Kloth – has tools to monitor domain and DNS (my favorite)
MX Toolbox – tool to check your email (MX) records which is useful when you’re installing google apps
Traceroute - allows you to test your IP from various locations around the world, this comes in handy when you are changing hosts and want to know which host is live with your website
InterNIC Whois – one of the reliable sites to show whois info for a domain name
