Bethesda has revealed details about the new DLC that is set to release sometime in January. The DLC will give you four to five more hours of gameplay and it is called Operation: Anchorage and it will set you back 800 MSP.
Operation: Anchorage is a military simulation that exists to help the government run counter offensive training should the Chinese red army rise to power again.
Bethesda also plans on new DLC to roll out in February and again in March. The February DLC will be named the Pitt and that will add a Raider town in the remains of Pittsburgh. The March DLC is named Broken Steel and that will let you play after the completion of the main quest.
Fallout 3 DLC is set for Xbox 360 and the PC and there is no plan for the PS3 extras.
I really enjoyed Fallout 3 (not that I have finished playing totally) and will probaly be checking out Operation: Anchorage, and the March DLC is something I will also look into so you can continue to play after the main quest.