Ever wondered who is hosting those high-traffic websites like BoingBoing, TechCrunch or the Drudge Report ? Enter a website address here and the tool will return name of the web host provider that's hosting that website or blog. You can then use Bing to determine other sites hosted on a server.
Also see: Know Everything about a Website
You may be also interested in the following domain name and DNS information tools:
Netcraft Web Server Query - Type a website URL and Netcraft will tell you the site's operating system, web server, and a graphical view of the time since last reboot for each of the computers serving the site.
DomJax [review] - Checks domain name availability and also runs an automatic whois report for any domain that's taken - hover the mouse over the domain name and DomJax pops up a neat "thought bubble" which has all the information about that domain like who owns it, when it will expire and how to contact the owner.
AJAX DNS - An excellent set of common DNS commands and tools packed in a non-geeky interface. See all DNS records and Reverse DNS records for a domain, HTTP headers, ping a domain or view the whois details for a domain.