Apparently only James Cameron knows the secrets to grossing a billion dollars at the box office, given that both movies sitting in the top two spots were written and directed by him. Whatever you opinion of the man, there's no denying the fact that he's tapped into something that so many other directors have not - the ability to sell his movies to the entire the world. Avatar is, of course, the highest-grossing movie of all-time - and there's no reason that it won't stay that way for a while. It's true that Avatar probably doesn't contain anywhere near as many obviously "iconic" scenes as Titanic (Cameron's other billion dollar movie, in you case you didn't know), but for our money the sequence where hero Jake realises his dreams of flying has come to define the magic and majesty that is Avatar: the special effects are out of this world; the moment is rich and emotional. It's a credit to James Cameron the director, and is surely the most iconic part of the film.
Sam Hill is an ardent cinephile and has been writing about film professionally since 2008. He harbours a particular fondness for western and sci-fi movies.