This fan-made mashup video has been kicking around the internet since July, but it's worth a look if you haven't seen it, especially if you've just finished reading our roundup of particularly grim westerns. It's the final shootout from Sergio Leone's Once Upon A Time In The West with the Arcade Fire's "My Body Is A Cage" used as the soundtrack instead of Ennio Morricone's original score. It's impressive how well it syncs up to the action and fits the mood of the scene. (Note: If you haven't seen the movie yet, this will spoil the ending.)
For comparison, here's the original version with Morricone's music behind it:
And just because it's my favorite gunfight scene, here's the masterful ending of The Good, The Bad, And The Ugly: