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.

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.