Ran across a nice article on six free security tools. While I would more accurately categorize some of these tools as "hacker tools" (since they don't directly improve the security of your network), they are useful nonetheless.
Check it out at:
Thomas W Shinder, M.D.
GET THE NEW BOOK! Go to http://tinyurl.com/2gpoo8
Email: [email protected]
MVP - Microsoft Firewalls (ISA)