Valve Community

F13.Net is a review site that ocassionally covers Valve’s games.

Cheesecake Servers is a small but dedicated community for Gmod and TF2.

Mod My What covers the modding scene with articles and news.

Type 3 Studios is a “studio” and home of a couple of mods and a collection of tutorials.

Nana’s Paradox covers Source games and runs articles and news about maps and mods.

The Sven Co-op Map Database is exactly what the title suggests; a database of maps for Sven Co-Op.

Thinking With Portals is a website dedicated to Portal and its custom maps.

Solid Surf is a site specific to the surfing aspect of CS:S, run by sintax error, and used mainly by the mapping studio solidsurf that he started.

Games On Net is a gaming portal for an Austrailian ISP. It covers lots of games, and has active forums.

Garry’s Mod.de is a German portal focused on Garry’s Mod.

OnlineGame.se is a Scandinavian site that covers Team Fortress 2.

TeamFortress2.fr is a French site that covers the TF2 scene.