As mentioned on Kotaku and Joystiq, Call of Duty 2 has just recently sold over 1,000,000 units. This is an excellent milestone for Microsoft as well as publishers because it shows that publishers can produce blockbuster titles can gross earnings in the tens of millions of dollars range on the next generation of consoles -- the implication of this being publishers will be less concerned with making features backwards portable in the interest of maintaining sales. Joystiq makes mention of Wikipedia's numbers for Xbox 360 games selling over a million copies:
Microsoft Xbox 360 games that have sold more than one million copies worldwide as of August 2006.
- Call of Duty 2 (1.32 million) 
- Tom Clancy's Ghost Recon Advanced Warfighter (1.28 million) 
- The Elder Scrolls IV: Oblivion (1.13 million)