Spywire Forums
Forum dedicated to bringing knowledge to people starting out in hacking. http://spywire.net/forum/index.php
Irvine Underground Forums
Discussion forum for Southern California security experts and hackers. [RSS] http://ivu.irvineunderground.org/
Social Engineering
Discussion forum about the insecurity of humans known as social engineering. http://www.socialengineering101.com
HFX International Forum
Discussion forum for topics surrounding the underground, technology and the like. http://forum.hfactorx.org/
SecureRoot
One of the worlds longest established hacking forums, offering resources covering everything from cracking to phreaking. http://www.secureroot.com
The Forbidden Web Archive
Security and Development Forum with a Security Basics Forum and Vuln-Dev. http://www.forbiddenweb.org/
HeapOverflow Computer Security Community
Computer security community with forums, blogs and directory covering exploit, vulnerability, advisory with various penetration testing tools. http://heapoverflow.com
The Computer Science Directory currently has categories, which include links along with indexed pages.