What are some alternatives?
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.
OpenDNS - OpenDNS provides faster and safer Internet access for your home or Business.
Google Public DNS - The Domain Name System (DNS) protocol is an important part of the web's infrastructure, serving as the Internet's phone book: every time you visit a website, your computer performs a DNS lookup.
NameserverChecker.com - Nameserver Checker Tool
NameserversTool.com - Nameserver Lookup Tool
NameserverFinder.com - Nameserver Lookup Tool