Garry's famous mod is now available on Steam for only $5! It's 50% off for the whole week. Get it while you can, it's a great gateway into the modding community, and it sure makes for some funny movies! Many game developers, like Epic Games and Insomniac Studios, have recommended using tools such as Garry's Mod to develop a portfolio worthy of hire. If that's not reason enough, then this is.
Team Fortress 2's more recent release gave Garry's Modders a great number of new possibilities, of which Steam has included the best in their official screenshots.