TF2 Maps is a community mapping site based around an active forum. It offers map downloads, tutorials, servers, developer blogs and user galleries.

The Whole Half-Life AKA TWHL is first and foremost a community of mappers and modders. It has very active forums and plenty of tutorials.

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.