Does your Team Fortress 2 backpack runneth over? With the newly launched Steam Trading Beta, you can turn your excess in-game TF2 items into other in-game items or, more importantly, a gifted copy of Left 4 Dead.
How does it work? Well, first, Steam users must first opt-in to the Steam Trading Beta. Then, should they have a Team Fortress 2 hat, weapon, badge, footwear item or can of Crit-a-Cola that another user may crave, they can trade said item for, say, a gifted copy of some other Steam game. Just look for other players who have opted into the beta via Group Chat or your Steam Friends List.
The system marries the already existing gifting of Steam games with Team Fortress 2 item trading, basically.
Right now, beta trading is limited to Team Fortress 2 in-game items and Steam Gifts (unplayed extra copies of games), but Valve says it plans to extend item trading to Portal 2 and third-party developers who are interested in managing in-game items and inventories through Steam.
There's a FAQ for this whole thing, if you'd like to learn more.
Introducing Steam Trading Beta [Team Fortress Blog]