Halo 3 has become the first Xbox title (on either the original or 360) to break 10 million copies worldwide as of the 8th August 2009 according to VGChartz research. This makes the title only the 35th game ever to reach this mark, the full list can be found here.
After launching to an astonishing 3.8 million copies in it's first week (a record which still stands) and with an average critic score of 9.6, long-term success for Halo 3 was assured. Nearly two years after launch, the game is still a regular in the worldwide weekly top 30 selling around 30,000 copies per week. In fact, the only reason why Halo 3 is likely to drop out of the top 30 in the coming months is due to the release of Halo 3: ODST - a side quest focusing on the Orbital Drop Shock Trooper. Preorders for that title are already well over a million in the US alone so it looks like Bungie will have another huge hit on their hands.