This deal has ended.
Update: This no longer works on games for pre-order, so Halo 3: ODST and Call of Duty are out. BestBuy.com has a great new promotion: Buy One XBox 360 Game, Get One 50% Off. This works on almost every game in their inventory (if you are choosing games that have different prices, the lower price receives the discount). Check out the newest $59.99 games:
Halo 3: ODST (pre-order), Madden NFL 10, Resident Evil 5, Fallout 3, Batman: Arkham Asylum, and Call of Duty: Modern Warfare 2. Also check out Gears of War 2 for $39.99, as well as The Orange Box and Tony Hawk's Proving Ground for $19.99 each. Shipping is free with sales tax charged in most states.