The 2nd DLC, Resurgence Pack, will be out on 3rd of June and will be an Xbox 360 exclusive for 30 days, just like the Stimulus Package. It will follow on the PS3 and PC sometime in July.
The Resurgence Pack will cost Modern Warfare 2 fans 15 USD (same as its predecessor) and will include five maps, of which three are new ones and the rest Call of Duty 4 remakes.
If the DLC isn't your thing, prepare for Call of Duty 7: Black Ops which will be out on 9th of November.