Domino Theory
Crystal Dynamics
Josh Hamrick did a lot of sandbox work as well.
I honestly don't think that COD's release date should or does have much of an impact on when MS releases the game. Lots of games sell extremely well during the holiday season, regardless of other games out there. Assassins Creed titles have released on the release date of COD or the week after for the past three years and they have sold extremely well..
Yeah and now Ubisoft has moved its stance from releasing AC a week after COD to a week or two before COD with AC3 this year.
Call of Duty's release matters because that's where most of the mainstream's attention will be. Halo and Call of Duty hit similar consumer demographics.