From this quote:
Originally posted by InfinityWard
“As far as DLC goes, we love it and plan to support ‘Modern Warfare 2′ heavily with post-launch support. We’ve confirmed we’ll be doing AT LEAST two map packs which were announced at E3 as a timed exclusive for Xbox 360. The fact that we confirmed at least two map packs doesn’t mean there won’t be more; honestly we plan on shaping our DLC based on community feedback from the full game, and first two DLC map packs. Therefore, the community will really determine what comes after that.”
There could be another map pack. Like it says, they'll try to make map packs considering our opinions and what not. I also heard there may be a weapons pack coming out. BTW why does XBL have the ability to lock their Private Matches while us PS3 guys have to sign out/in to lock? Is this in a DLC?