Major Nelson revealed today on his blog that Xbox Live Arcade is having a firesale of several Arcade titles that will be reduced in price of up to 50% on some titles. Here's the list of the those titles.

South Park 800 400 50%
Super Street Fighter II HD Remix 1200 560 53%
Defense Grid 800 400 50%
Rocket Riot 800 400 50%
Mad Tracks 800 400 50%
Track & Field 400 240 40%
Lumines Live 800 400 50%
Age of Booty 800 400 50%
Schizoid 800 400 50%
Wallace & Gromit episode 1 800 400 50%

Check out the news post on Major Nelson's Blog