Some very decent picks there, doffcocker.
When I think of the American Beauty soundtrack I think of that piano piece you mention and I also think of the harmony of Lennon and McCartney singing 'Because' as the film ends.
The Graduate arguably is the film with the best one-artist soundtrack ever made. It makes me emotional to think of Dustin Hoffman crossing (I think) the Bay Bridge, pursuing an unknown future, to the accompaniment of 'Scarborough Fair', or contemplating the futility of his affair to the sound of 'April, Come She Will' - I am a massive fan of both The Graduate and Simon & Garfunkel. I saw S&G live at the MEN about 10 years ago. I visit Widnes railway station quite often to watch rugby, there used to be a plaque there as it's where Paul Simon wrote 'Homeward Bound', stranded on the platform over night there, but unfortunately the plaque keeps getting stolen. Widnes is a bit too close to Liverpool.
The Graduate is a great film for anyone who wants to get an idea of film theory to watch. There is all sorts of clever stuff in that film created by Mike Nicols. There's a scene in a hotel room where Benjamin and Mrs Robinson argue about their relationship. Benjamin is 'framed' by a doorway which splits the shot in two. If you look closely there is a shadow of a candle on Mrs Robinson's side of the shot which resembles a phallus, symbolising that she has the sexual power and control in their relationship. I also really like the bit where Benjamin follows Elaine to the zoo and she meets up with Carl, and they leave Benjamin on his own. He makes eye contact with a lonely looking orangutan which is in an enclosure on its own. The orangutan itself is looking enviously across the way at two other primates who are an obvious male/female pair. It's just beautifully done. I also love the use of symbolism involving water in that film.
Trainspotting also has a great soundtrack, more of a fan of Iggy Pop than Underworld. Though I was about 18 when that film came out and that track was popular in the clubs, don't know if it is still is, but I associate it with clubbing. It's interesting to me how there's now a generation of British people in their 20s and 30s now who automatically associate the song 'Perfect Day' with Ewen McGregor lay on the floor overdosing on heroin. What would Lou Reed have thought? It's a great example of how effective use of music can actually 'change' the song's meaning for people.
I thought the soundtrack to Kill Bill Volume 1 was probably the weakest of the Tarantino soundtracks, not in terms of how well the tracks worked in the film - I thought they were very effective - but as a standalone album, it was quite tedious. That Nancy Sinatra track is a delight though. It goes to show that a soundtrack can unify a film well but not necessarily an album, I just thought it was disjointed.