Modern Warfare 2 player. Just a few minutes ago, the "Stimulus Package" DLC bundle, which includes three new multiplayer maps and two tarted-up arenas from Call of Duty 4, went live on Xbox 360. At $15, it's a pretty pricey prescription for your blues, but it might just be the only option you've got. Curse you, pharmaceutical empire!
Unfortunately, it seems the launch of the new maps was botched -- we've received a number of tips claiming the maps aren't loading in-game. Major Nelson recently Tweeted that the game needs a title update in order to incorporate the new content, which he says is coming soon. We'll let you know when everything's in working order.
Update: The Major just confirmed that the title update is live, and should be available worldwide in "a few minutes."