AntiVirus

Symantec  

• Security Response - Latest info on virus' and worms
• Virus Encyclopedia - Excellent source for verifying virus hoaxes

Trend Micro

• Security Information - Current status, weekly report, encyclopedia, virus map

Microsoft

Microsoft Security - Microsoft Security Home site.

• Hotfix and Security Bulletins 
• Security Tools & Checklists
• Windows Update

Information Security Sites

Security Focus - Maintainers of the BugTraq mailing list, and one of the largest security databases on the Internet.
Packet Storm - Another large security portal site.
Counterpane - Bruce Schneier, author of Applied Cryptography and Secrets and Lies.
@Stake - Old L0pht crew.
Information Security Magazine - "The authority in security news, insight and analysis."
The Honey Net Project- Learn the tools, tactics, and motives of the blackhat community.
Linux Security - Linux security portal.
VulnWatch - Vulnerability announcement site.
ntsecurity.nu - Arne Vidstrom's site
CSO Online - Security site targeted at Chief Security Officers.
Search Security - "The Web's best security-specific information resource for enterprise IT professionals"
Sys-security - Ofir Arkin's site, home of the "ICMP Usage In Scanning" research project.
Whitehats - Online community resource to provide support for those who are interested in network security.
Nessus - Home of Nessus, an open source security scanner.
Snort - Open source Network Intrusion Detection System.
The Encyclopedia of Computer Security

Organizations

CERT - Computer Emergency Response Team (Carnegie Mellon University)
CIS - The Center for Internet Security
COAST - Computer Operations, Audit, and Security Technology (Purdue University)
CSI - Computer Security Institute
DHS - Department of Homeland Security
DShield - Distributed Intrusion Detection System
FIRST - Forum of Incident Response and Security Teams
ISC - Internet Storm Center
ISECOM - Institute for Security and Open Methodologies
NIPC - National Infrastructure Protection Center
NIST CSRC - National Institute of Standards and Technology, Computer Security Resource Center
US DOE-CIAC - US Department of Energy, Computer Incident Advisory Committee
SANS - System Administration, Networking and Security Institute

Incident Response

CERT - Computer Emergency Response Team (Carnegie Mellon University)

• Handbook for Computer Security Incident Response Teams (CSIRTs)
• Computer Security Incident Response Team (CSIRT) Development
• Detecting Signs of Intrusion
• Responding to Intrusions
• Unix Intruder Detection Checklist
• Windows NT Intruder Detection Checklist

Web Development

OWASP - Open Web Application Security Project
CGISecurity - Secure web programming site.

Adware, Spyware, and Parasites

www.doxdesk.com
Counter Exploitation - Adware page on Counter Exploitation
www.spywareguide.com - Information about spyware and adware
www.spychecker.com - A public database of Spyware products.

Hoaxes and Scams

Hoax Busters - Covers the gamut of all types of hoaxes.
Top 10 Web Scams