Over the last week or so, I have got sidetracked to a couple useful tools.  First one is a decent WhoIs that provides quite a bit of information about a domain such as:

* Evaluation of meta information on the site
* RSS feed detection and list
* Possible releated sites
* DMOZ listings
* Vistors number by country (and by city on some sites)
* Alexa rank
* Compete.com rank
* Yahoo listings
* Wikipedia pages referrencing the domain
* Server information
* Registrar information
* IP, Whois and Name server history

Quite a bit of information on a site along with other side line information.

http://whois.domaintools.com

Next one is for Reverse IP lookup.  That is the process of finding what sites are running under the same IP.  There are a ton of them out there and some sites charge for this feature, but I found one that is free and provides not only the list of sites on that single IP address but also the list of sites listed in the name server used by the domain.  Pretty handy information:

http://domainsdb.net