Tweak Guides provides incredibly useful information and tips on how to get the most out of your hardware and games.

UberCharged.Net contains random crap referring to TF2, hopefully vaguely entertaining.

It might seem strange to add Wikipedia to this directory but it contain some very useful information for Valve’s fans. The sections on the games are very detailed. It is also available in many langauges.

World Of Level Design is a website/blog aimed at those interested in Environment Art and Game Level Design. It contains plenty of original content, including tutorials, articles and interviews. There is also a lively forum.

Zombie Panic: Source is a survival horror MP HL2 modification. Play as either the survivors or the undead, trying to wipe each other out or completing objectives to escape the horror.