Screaming Penguin - Source Does Matter

This list has apparently been around a while, but this is the first I have seen of it and its good stuff.
Insecure did a survey of security tools used by users on the nmap mailing list. Then they compiled
the top 50 into this list: http://www.insecure.org/tools.html.

Checkit and also, this goes without saying pretty much, but make sure you have nmap handy at all times!   http://www.insecure.org/tools.html