Attrition.org: Attrition is an eclectic collection of internet and computer security resources.
Crewl Underground Madness: Belgian group specialized in computer and network (in)security, hacking, coding and phreaking.
Cult of the Dead Cow: Offers blog, team background, tools and BackOrifice downloads, and news archive.
Digital Information Society: Exploit archive, phreaking information, and group member pages.
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.
enZo: Coding group. Offer hacking tools and vulnerability exploits.
HackHull: Group of hackers in the United Kingdom. Information about meetings, projects, and links to personal pages.
HATE (Hackers Against Tyranny Everywhere): Anarchy, HAcking, Phreaking files for newbies.
Moloch Industries: A New York hacker group.
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.
Progenic Security: Security advice and exploits.
Pulhas WebSite: A collection of current hacker news articles.
Razor: Team of security researchers. Features news, original papers and advisories, presentations they have given, and tools they have written.
Synnergy Networks: Security research site with quality papers and exploits
Toxyn Technologies, Inc.: Hacking related group.
Twentythreedotorg: SoCal's hacking group. Canadian free since 1999.
TwistedinterneT ServiceS International Inc.: Underground Hacker site with an extensive archive and library.
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.