$600 million: The box office mark passed by "Marvel's The Avengers" on Tuesday. It is not one of only three films to ever cross that mark. The other two? The James Cameron-helmed "Avatar" and "Titanic." The film has only been in theaters for 54 days. What film did it surplant at No. 3? "The Dark Knight." We'll see if "The Dark Knight Rises" can make its way to the top.