Vulnerability scanner does automated search for security weaknesses in web applications, computers and theirs services and reports them in details about possible vulnerabilities and probable defense or ways to prevent it.

This is a list of both commecial and free scanners out there. It is hard to rate which is better than other so there will be no ratings or comparisons but only listing of vulnerability scanners:

http://www.windowhaxor.net/2007/09/2...lity-scanners/