Groups

Attrition.org
Attrition is an eclectic collection of internet and computer security resources.
http://attrition.org/

Crewl Underground Madness
Belgian group specialized in computer and network (in)security, hacking, coding and phreaking.
http://www.blackhat.be/

Cult of the Dead Cow
Offers weblog, team background, tools and BackOrifice downloads, and news archive.
http://www.cultdeadcow.com/

Digital Information Society
Exploit archive, phreaking information, and group member pages.
http://www.phreak.org/

Eleventh Alliance
Offers details regarding select viruses, overflow and security exploits, bios tools, and crytography. Also features book reviews on assembly programming and computer security.
http://www.11a.nu/

enZo
Coding group. Offer hacking tools and vulnerability exploits.
http://www.enzotech.net/

HackHull
Group of hackers in the United Kingdom. Information about meetings, projects, and links to personal pages.
http://www.hackhull.com/

HATE (Hackers Against Tyranny Everywhere)
Anarchy, HAcking, Phreaking files for newbies.
http://hnsg.net/

Moloch Industries
A New York hacker group.
http://www.moloch.org/

Nomad Mobile Research Centre
Hacker lab engaged in vulnerabilities research. Security papers, full disclosure advisories and current projects. Also features a FAQ on hacking techniques.
http://www.nmrc.org/

Progenic Security
Security advice and exploits.
http://www.progenic.com/

Razor
Team of security researchers. Features news, original papers and advisories, presentations they have given, and tools they have written.
http://www.bindview.com/Services/Razor/

Twentythreedotorg
SoCal's hacking group. Canadian free since 1999.
http://www.23.org/

Xfocus
Organization dedicated to the research and demonstration of vulnerabilities in network services and communication security. Offers papers, security tools, exploit code, advisories and a discussion forum.
http://www.xfocus.org/