Dig is an old standby DNS utility. As internet technologies have matured, the use for dig has gone down, but it's still very useful for finding out who owns which domains or IP's and where they point on the internet.
I always forget what dig means, so of course, I consulted the DNS wiki, reminding me that dig is the "domain information groper". True name...I couldn't have made up anything better than that.
My favorite dig site is menandmice. Very simple, straight-forward and a good one to bookmark. Use it to confirm DNS configurations or find out what's going on behind the scenes on a site. To see an example of a fairly confusing DNS configuration, look up yahoo: http://www.menandmice.com/cgi-bin/DoDig?host=&domain=www.yahoo.com&type=A&recur=on. You'll see that they CNAME (or alias) their www site to Akamai, which has DNS servers all over the world (providing speedy, redundant and DOS-proof (mostly) DNS).
Why is this interesting? DNS is a core foundational component of the internet. All web requests must first be resolved by DNS. In order to make web analytics data collection fast and reliable, everyone must have a reliable DNS infrastructure and really understand how it works. Dig is a great tool for taking a closer look.