Xbox Live's Games on Demand service gains several new games today. Most notable among the four titles is probably Vanquish, which can be had for a steep $40.
DiRT 2 is also available for $30, while either Velvet Assassin or Operation Flashpoint: Dragon Rising can be had for $20.
Vanquish $40 [Xbox.com]
DiRT 2 $30 [Xbox.com]
Velvet Assassin $20 [Xbox.com]
Operation Flashpoint: Dragon Rising $20 [Xbox.com]