We’ve covered a couple of DNS tools in the past, such as the DNS propagation checker, which are useful for anyone that owns a domain. The problem is that you generally have to jump around to a bunch of different sites in order to do simple things like reverse IP lookups, traceroutes, Chinese firewall tests, propagation checks, and more. Normally you need to find a site that is dedicated to do each of those things, but ViewDNS.info pulls that all together into a single site with a simple interface.
This site makes it extremely easy to perform all of the things I mentioned earlier plus some. In fact it has over 20 different tools you can use on any domain and IP address you might have. Many of the tests, such as the DNS report, are essential tools for determining the health of the DNS for your site.