Bethseda has announced downloadable content for Fallout: New Vegas, all due to be avaiable for PC, PS3 and Xbox 360 users at the same time (so no worries about access being delayed for any platform).

Honest Hearts is the first, due out on May 17 and featuring Utah's Zion National Park.  Your travelling caravan will be attacked by a tribal raiding band, leaving you to pick up the pieces battling enemies, making decisions and dealing with a person known as the 'Burned Man.' 

Old World Blues comes out sometime in June.  In it, you'll finally discover exactly what happened to change Bessie the cow into the twisted mutated monstrosity she is today, scouring through old research facilities while dealing with possible friends and foes.
And finally, in July Lonesome Road will be released.  In it, you'll encouter Ulysses.  Don't know who he is? Remember the original Courier Six? Yeah, that guy, responsible for a lot of issues that you had at the begining of New Vegas.  He offers an explanation: for a price.  One last job that will take you into places that few if any have returned from.

DLC will be 800MS Points, $9.99 on the PSNetwork and $9.99 for Steam and Direct2Drive.