HL2 Gets a Sneaky Oculus Rift Support
Though the support isn't entirely officially released yet, lucky owners of the goggles can already test it out with Half-Life 2 by entering the SteamPipe beta (right-click HL2, select Properties, go to the "Betas" tab and opt in for the beta). You'll need to edit your game's launch options by adding "-vr" to the end of the command line. This is also done in the Properties window.
The official release is set to release sometime in the next few weeks. Just keep in mind that we're talking about Valve here.