http://www.netcraft.com
A guy in one of my classes showed this to us this morning. Plug in any host name/web address and it digs up all sorts of cool info. Like doing nslookup and whois all at once, plus more. They even have a toolbar you can use to check any site you happen to be on. Pretty cool, yet kind of scary. They also have historical info. For example, I looked up a domain I have registered and used to host on a machine at home. It found the current host server, IP, etc, and also the old IP, even the version of Apache that was running on that server.