I recently added the 1995 movie "Dead Man" to my list of movies-I-need-to-see-but-have-heard-the-soundtrack-to. It grows and grows and grows.
I don't know anything about the movie but for the liberal use of film excerpts. Normally I'm not a fan of dialogue over music in soundtracks, but it fits Neil Young's ambient, improvised guitar jahms like a glove.
The soundtrack was recorded in one take, with Neil Young improvising while he watched the film. And, since he's Neil Young, Neil Young plays his slow, grungily atmospheric guitar in such a manner that I don't need to see the movie at all.
Edit: And now people are saying that Gibby Fucking Haynes is in this movie? I need to see it right now.