Another free tool for checking the safety of unknown website is LinkScanner from Exploit Prevention Labs. You just type the address of the website into the form and LinkScanner visits the site and checks its links to see if any of them lead to known malware websites. XPL also offers a free Lite version of the software that can be installed on your computer as well as a Pro level version which retails for $29.95 for a one-year subscription. The Pro version received 7.5 out of 10 (very good rating) from cnet.com in February 2007.

Exploit Prevention Labs was acquired by Grisoft, the maker of the AVG line of anti-virus products, in December 2007. I imagine much of LinkScanner's capabilities will be integrated into the various Grisoft/AVG products in time.