http://fallout.wikia.com/wiki/Dead_Money
"Dead Money is the first add-on for Fallout: New Vegas, developed by Obsidian Entertainment and published by Bethesda Softworks, to be released on December 21, 2010 for the Xbox 360 platform."
And thank god. This probably means we'll have some quests that are actually memorable and non-linear, instead of something like O:A.
Well, you Xbox 360 owners will have what is listed above.

For a time anyways. I'm sure the rest of us on the PC or PS3 will get it later.