http://whois.domaintools.com/ has been my long term favorite domain lookup tool for things like blacklist status, IP location, registrar information, etc. , but now it has a lot more information including search engine optimization (SEO) score, number of visitors by country, number of visitors per month, contact info and much more.

 

But now there are a lot of new tools that might be of interest – My IP Address, Traceroute, Domain Search using a partial name, Network Ping, Domain Monitor and more.  Check them out at http://www.domaintools.com/services/.