Bethesda has announced that DLC for New Vegas, called Dead Money, will be available for the Xbox 360 version only on December 21st.
The official blurb, minus the fact that Bethesda is very excited, is "As the victim of a raw deal you must work alongside three other captured wastelanders to recover the legendary treasure of the Sierra Madre Casino. In Dead Money, your life hangs in the balance as you face new terrain, foes, and choices. It is up to you how you play your cards in the quest to survive."
It's going to cost you 800 Microsoft points.