42nd Street (1933)
Directed by Lloyd Bacon
Poster Designed by Hubbard G Robinson & Joseph Tisman
Film Nationality - USA
Poster Nationality - USA
A poster that routinely makes these sorts of lists for good reason is this one for Lloyd Bacon's 42nd Street. It made #47 on the American Film Institute's list, too. This musical is famous for it's classic Busby Berkley choreography (other than being a superb film in general) and it this feature that makes the poster so great and iconic. Using the movie famous part of the movie - the camera pan through the the legs of the chorus line - immediately gives the poster an eye-catching and discussion-starting design.
The other thing I like about it is that they give all the cast their due, putting their faces in little bubbles at the side. It's a nice way of showing off your entire cast without overly crowding the design, which so many posters do these days.
The whole design just has a joyous energy about it that befits this musical masterpiece.