Valve has offered a treat to Linux users with the release of a Left 4 Dead 2 beta. A Portal beta for Linux is also available, but Valve has been a bit mum on that release. If you own any of those three games, the betas should appear in your Steam library.
The Left 4 Dead blog announced the release, revealing that they will use this build as a testing ground for the Extended Mutation System for script authors. Players will also get access to the authoring tools and the beta dedicated server. The Linux version is the same size as the original game, so go grab some food while you wait for the download.
BluesNews is also reporting that the Linux versions of Portal has started showing up in user libraries as well, so check for it if you own the game.