Chats and Forums

The Forbidden Web Archive
Security and Development Forum with a Security Basics Forum and Vuln-Dev.
http://www.forbiddenweb.org/

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

Social Engineering
Discussion forum about the insecurity of humans known as social engineering.
http://www.socialengineering101.com

Irvine Underground Forums
Discussion forum for Southern California security experts and hackers. [RSS]
http://ivu.irvineunderground.org/