Microsoft Store offers Street Fighter IV for Xbox 360 for $19.99.  Apply coupon code "CLR-MSFT-Games-50%" to lower it to $10.  Shipping adds $4.99.  This is the lowest total price available by $5.

The Microsoft Store offers Call of Duty: Modern Warfare 2 for Xbox 360 for $41.99 (30% Off), with free shipping.  This is the lowest price available by $7.  Sales tax added where applicable.