Halo: ReachDefiant Map PackCall of Duty: Black OpsWorld of WarHalo 2
Condemned: 
Unearthed:teabag each other
Highlands:

The Defiant Map Pack will be available on Xbox Live for 800 Microsoft Points and will include new achievements that can pump your Gamerscore up by a total 150 points. Assuming you're not into things like "free time" and "other games," of course. Peep the trailer below. [via Major Nelson]