Brief Encounter (1945, dir David Lean), Rachmaninov’s Second Piano Concerto. One of the most romantic movies ever made, Rachmaninov fits perfectly.
Raging Bull (1980, dir Martin Scorsese), Mascagni’s opera Cavalleria Rusticana. Opening scen, very surprising since the music its very far away from the theme of boxing, yet it works.
2001: A Space Odyssey (1968, dir Stanley Kubrick) Johann Strauss II’s Blue Danube Waltzand Ligeti’s Requiem and Lux Aeterna, but it’s Richard Strauss’s Also Sprach Zarathustra (performed by the Vienna Philharmonic under Herbert von Karajan).