The following are some North American top 10 lists of units sold relative to the install base for the particular console system(s) the titles were released for. In other words, the percentage states the percent of owners of a particular console that bought the game.
Xbox 360 (8,805,238 systems sold)
1. Halo 3 (47.4%)
2. Gears of War (34.4%)
3. Elder Scrolls IV: Oblivion (15.9%)
4. Guitar Hero II (15.4%)
5. Forza Motorsport 2 (15.0%)
6. Madden NFL 08 (14.7%)
7. Marvel Ultimate Alliance (13.8%)
8. Rainbow Six: Vegas (13.8%)
9. Call of Duty 3 (13.4%)
10. Fight Night Round 3 (12.7%)
Aside from Halo 3 and Gears of War, although the attachment rate of the other top selling games are only within the 12 - 16 % range, when considering the number of 360 owners, there are quite a few games selling a lot of units. With the way Guitar Hero III, Assassin's Creed, and Call of Duty 4 have been selling, it is likely that they will soon land a spot on this list.