Left 4 Dead 2 is free on Steam today
Valve isn't Santa, but the company is pretty darn close. In addition to the Holiday Sale, Valve is giving away Left 4 Dead 2 for free on Steam today.
Users have until 10am PST tomorrow, December 26th to claim the gift -- all you need to do is install it and it is yours to keep forever. If you don't install it, it will go back to its regular price.
Additionally, all current players have the chance to earn the "Ghost of Christmas Present" achievement by helping a free holiday player survive a campaign.