"Don't have TF2? Want to play it anyway? Valve is hosting a free play weekend for all you slackers:
A worldwide Team Fortress 2 Free Weekend is now under way! Join now, and play the full game for free, including the new content just released in the TF2: Gold Rush Update.
The Free Weekend is open to players around the world, and there is no obligation to purchase to participate; all that is needed is a Steam account to join.
To join in the fun and learn more about Team Fortress 2, please visit www.steamgames.com/goldrush
The Free Weekend ends Sunday, May 4th at 1pm PDT."