What are the most influential movies ever made?

[Cabby]

Movies that influence future screenwriters and directors for example and are often cited as "influential films"...

For example, Christopher Nolan has often cited Blade Runner as a major influence on Batman Begins in terms of it's visual design and romanticism.

Tarantino was clearly influenced by films like Death Rides A Horse (Kill Bill) and Bande a Part (Pulp Fiction).

The construction and style of films like Citizen Kane, Metropolis, The Birth of a Nation, and Battleship Potemkin have often been paid homage to.

In terms of modern cinema look at The Dark Knight. That film is hugely influential in the fact that it raised the bar of the superhero genre. They are held at such a high standard now. Ever since the massive critical and financial success of the film it seems like studios are wanting their superheros to be "dark and gritty" ala The Dark Knight.


So... what influential movies can you think of?