Robtex - See if your IP Address or host name is blacklisted. Also reports on DNS configuration issues.

 

SpiceWorks - Software monitoring  tool. Free program creates lists of all PCs and software on your network, and tracks licenses, warranties, and serial numbers.

 

SiteAdvisor - Web safety tool that helps keep you safe from adware, spam, and online scams. SiteAdvisor only works with Internet Explorer.