Established in 1988, the CERTŪ Coordination Center (CERT/CC) is a center of Internet security expertise, located at the Software Engineering Institute, a federally funded research and development center operated by Carnegie Mellon University

SANS is one of the most trusted and by far the largest source for information security training and certification in the world. It also develops, maintains, and makes available at no cost, the largest collection of research documents about various aspects of information security, and it operates the Internet's early warning system - Internet Storm Center.

SecurityFocus is a vendor-neutral site that provides objective, timely and comprehensive security information to all members of the security community, from end users, security hobbyists and network administrators to security consultants, IT Managers, CIOs and CSOs.

A good source of Unix related information for system admins. Lots of how-to's and more links to interesting stuff...

The BigAdmin portal is a Web-based, community-driven repository of resources specifically for system administrators -- by sys admins.

This web site is designed to act as a central source of Linux information and as a voice for the promotion and advocacy of the Linux operating system.