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

Whether you’re building a “Triple-A” commercial project or a mod for Half-Life® 2 , you’ll want to sign up as a Valve developer today.

This is the official home of Valve.

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.