Hackers.Com - Security related. (Resource)
Insecure.org - nmap, other tools, news... (Resource)
Netsec.Blogspot - Security News Blog (News)
New Order - Computer and Networking Security Portal (Reference)
NVD - National Vulnerability Database (USA) (Reference)
OSVDB - Open Source Vulnerability Database (Reference)
Rainbow Series Library - Rainbow Books (Documents)
SysNumbers - Well known numbers on various OSes and architectures (cpu, stack address, mmap, etc.) (Resource)
Security Focus - Vuln Database, Mailing lists (BugTraq), tools (Resource)
Slashdot - News for Nerds on the Stuff that Matters (News)