Software

Insecure.org: Top 75 Security tools
List of 75 security tools based on a 2003 vote by hackers.
http://sectools.org

Metasploit Project
Open-source platform for developing, testing, and using exploit code. Downloads and release notes. [Windows, Unix]
http://www.metasploit.com/

Rootkit
A program for hacking root.
http://www.rootkit.com/