Square Enix is holding a sale this week on the Xbox Marketplace, taking half off DLC for Deus Ex: Human Revolution and Just Cause 2, along with discounts on several of Lady Croft's adventures and its associated DLC.
The highlights of the sale are certainly the Deus Ex's Missing Link DLC and co-op adventure Lara Croft and the Guardian of Light for 600 MSP ($7.50). There's also some attempted discounts on full downloads of Battlestations: Pacific, Just Cause 2 and Tomb Raider: Underworld; but chances are you can find better in your local bargain bin.
Another game worth checking out is updated original Tomb Raider: Legend: Anniversary, available in two chunks at 400 MSP ($5) apiece (caveat is you'll need to own TR: Legend since it's the DLC). So, try the first two levels before you buy the whole thing. Find the full list of discounts after the break.