what will be 360's 10th game to reach 2m sold
http://vgchartz.com/games/index.php?name=&console=X360&publisher=&genre=&keyword=&order=Sales
my two candidates are
Call Of Duty 2 - 1.99 (it has to reach 2m soon)
Guitar Hero 3 - 1.56m (selling the most per week out of all the games over 1.5m)