I also like many of Ennio Morricone's film scores. I think he was influrntial to much of the later Beatles music in that he turned ordinary everyday objects into musical instruments. As well as the aforementioned I like Once Upon A Time In the West and Days of Heaven. I also like Maurice Jarre's score for Ryan's Daughter.
Alex North wrote a complete score for the film. The decision to add the classical works was post production. They no doubt played a major part in the success of the film.
John Williams did with sound what Richard Attenborough did with mirrors at the end of 'Oh what a lovely war'. The soundtrack of Star Wars was recorded several times with a small handful of musicians. Then Anvil Studios (That he was a director of), combined them to give the illusion of a full symphony orchestra. He was without doubt one of the most talented musicians who I ever worked with.