Looking through the Fall release dates...I think it is a given that the best selling game for their respective month (Aug-Dec) will be on the X360.
Aug - Madden 2010 8/14/09, this is an annual thing so 100% sure
Sep - Halo 3 ODST 9/22/09, it is Halo (Marketing, Marketing, Marketing) 100% sure
Oct - It is either going to be Forza 3 10/27/09, Splinter Cell Conviction 10/20/09, or Halo 3 ODST. These are the only major games coming out in Oct (in the case of ODST, the momentum could carry over from Sep like what Halo 3 did.). 95% sure
Nov - Modern Warfare 2 11/10/09, I think everyone in the world knows MW2 will be the biggest selling game this year. 1000% sure
note: you also have 3 others great games coming out on the X360 in Assasin's Creed 2, Bioshock 2, and L4D2. All 3 of them will be in the TOP 10 in Nov. 99% sure
Dec - Again December will be dominated by a COD/MW game just like the last 2 years.
