Sans: Site for information security research, certification and education.
http://www.sans.org/
Incidents.org: Monitors the data flowing in from the Storm Center analysis and coordination centers (SACCs) using automated analysis and graphical visualization tools and searches for activity that corresponds with broad based attacks. It also compares traffic patterns among the SACCs to determine whether certain industries are experiencing unique patterns of attacks. It reports its findings to the entire Internet community through the SACCs, through ISPs through national cyber defense organizations in countries around the globe and through more general postings and emails.
http://www.incidents.org
CERT Coordination Center: Is a center of Internet security expertise and is a federally funded research and development center operated by Carnegie Mellon University.
http://www.cert.org
Infosyssec: A comprehensive computer and network security resource.
http://www.infosyssec.com/
Cisco advisory page: Security Advisories are provided for security issues that directly impact Cisco products and action is necessary to repair the Cisco product.
http://www.cisco.com/en/US/products/products_security_advisories_listing.html
CheckPoint advisory page: Smart Defense Advisories provide technical information and mitigation methods against newly discovered vulnerabilities and exploits.
http://www.checkpoint.com/securitycenter/advisories/index.html
Microsoft advisory page: Microsoft advisory page: Security Advisories are provided for security issues that directly impact Microsoft products and action necessary to repair the affected technologies, solutions or product.
http://www.microsoft.com/technet/Security/default.mspx 
