In a time that seems like forever ago at the Tokyo Game Show, Microsoft announced that they Xbox 360 will be region coded, but it looks like it has been left up to the publisher to region code their titles or not, and some of them are chosing not to and thus work just fine on the Japanese and UK version of the console.
I am not sure of the validity of these claims, but the supposed region-free titles discovered include Call of Duty 2, Condemned: Criminal Origins, Gun and Tony Hawk: American Wasteland.