According to Dan Amrich of the Activision blog, there will be at least three new Call of Duty games in the next two years. This doesn't really come as too much of a surprise, since it is Activision, but each of the three will be handled by different teams according to his statement.
Amrich had this to say on the upcoming titles, "As for COD, they've confirmed three games in the next two years. Seeing as how there is a pattern of one new COD game every year, this is one new COD game from one new developer, and in a different genre from the core games we've seen."
So, of course the next title will be from Treyarch, and one will come out of Infinity Ward, providing they still exist in the near future. The third title is still a mystery, but speculation is that this third studio will be the recently founded Sledgehammer Games. Either way, maybe Activision should really slow down on overdeveloping titles, since we all know how well Guitar Hero has been going over, or even Tony Hawk for that matter.