Oh Brother Where Art Thou/Cold Mountain--instant classics.
24 Hour Party People--if you weren't there, this will make you wish you were.
Groove--I could have danced all night long.
Jackie Brown/Pulp Fiction/the Kill Bills--Tarantino knows what's good, and he knows what's cool, and he knows what's cool because it's good.
Go--soundtrack makes this movie.
Trainspotting--no comment necessary
Shaft/Superfly/Black Caesar--made the whole movie soundtrack thing popular. I mean, Isaac Hayes, Curtis Mayfield and James Brown...? studio execs took note...that was too much money to ignore.