What Agatha Christie books have two different titles?

Quite a few, actually. The reason for this is that American book publishers regularly rename books written by English people. I don't know why they do so, but they do. As a result, "Murder on the Orient Express" was sold in the US as "Murder on the Calais Coach", "Death in the Clouds" as "Death in the Air", "One, Two, Buckle my Shoe" as "The Patriotic Murders" and also "An Overdose of Death", "After the Funeral" as "Funerals are Fatal", "Dumb Witness" as "Poirot Loses a Client" and also "Mystery at Littlegreen House", "4:50 from Paddington" as "What Mrs. McGillicuddy Saw!", "Five Little Pigs" as "Murder in Retrospect" and so on and on.