Living in Canada, I know its going to be a bit longer (but hopefully not by much) before I see Xbox 360 posters and promotional displays in stores, but some in the US should be seeing them soon, as Microsoft has sent out the material.
Xbox Circle has the story:
With the console launch less then two months away, Microsoft has begun sending promotional material to retail stores world wide.
Microsoft has sent out promotional material to many retailers to begin the Xbox 360 marketing blitz. Stores like Best Buy, Target, and Circuit City have all received posters showing an Xbox 360 sitting above an Xbox with the words “heir to the throne.” Other promotional materials include take-home card cut outs of the concave design of the console.
As reported here last week Microsoft and Rare will also begin a huge Perfect Dark Zero promotional blitz beginning early October, so be sure to keep your eyes peeled.