Daniel Day Lewis did a pretty good "American" accent in "The Last of the Mohicans," but then I don't really think we have any idea how people sounded in those days. Probably pretty English--or wherever else they came from.

Sean Connery played an Arab with a Scottish accent in "The Wind and the Lion." I was in hysterics over that, until I looked it up and discovered the movie was based on a real incident, and the guy Connery was playing was the son of an Arab father and a Scottish mother, who taught him English.

In the original book, "The African Queen," Humphrey Bogart's part was a Cockney, but in the movie he was Canadian. I'm guessing Bogie wisely opted out of trying to do Cockney.