APress

Good source of ebooks and print books.

 AV-Test

Anti-virus research and data security

 CERT

Computer Emergency Readiness Team

 Chicken of the VNC (OS X)

VNC for the Macintosh

 ClamAV

Open source antivirus tool

 Current IP Check

Simple tool to show your real-world IP address.

 DNS Stuff

Various DNS and Spam lookup tools.

 DNSStuff

Various DNS and Spam lookup tools.

 EICAR

European Institute for Computer Antivirus Research - Antivirus research group that also has a standard "test" virus which is a harmless "virus" used to test virus scanners.

 Ethereal

Network analyzer.

 FileZilla

Open source FTP client.

 Firefox

Popular open source web browser.

 Free Software Foundation

The Free Software Foundation (FSF) is a nonprofit with a worldwide mission to promote computer user freedom and to defend the rights of all free software users.

 FreshMeat

Index of open source software.

 HotScripts

Index of open source software.

 HowtoForge

HowtoForge provides user-friendly Linux tutorials about almost every topic.

 IANA

The Internet Assigned Numbers Authority (IANA) is responsible for the global coordination of the DNS Root, IP addressing, and other Internet protocol resources.

 ICANN

Internet Corporation for Assigned Names and Numbers

 ICRA

Family Online Safety Institute - Internet Content Rating Association

 Internet Traffic Report

The Internet Traffic Report monitors the flow of data around the world.

 IS Alliance

Internet Security Alliance

 IS News

Internet Security News

 IS Policies

Information Security Policies / Computer Security Policies Directory

 Linux Documentation Project

Source of Linux guides and HOWTO's.

 Linux Foundation

The Linux Foundation promotes, protects and standardizes Linux by providing unified resources and services needed for open source to successfully compete with closed platforms.