Portal 2 50% off, celebrates free DLC release

To celebrate today's launch of free downloadable content for Portal 2, Valve has slashed the price of the puzzle title for a limited time on Steam.

Starting now and running until Thursday afternoon, a single digital copy of Portal 2 is priced at $14.99 (50% off).

New downloadable content for the game continues the co-op adventures of Atlas and P-Body. In addition, it adds new single- and multiplayer challenge modes. The DLC is also available on Xbox 360 and PS3 for free.

A two-game bundle is also available for $27.49 (50% off) as well as a set that includes the original Portal and its sequel for $17.49 (50% off). Check the Steam gamepage for details.

The promotion ends on Thursday at 4pm PT.