My favourite OST would have to be 'Donnie Darko'. This may seem biased because it's my favourite movie, but the soundtrack is one of the big reasons why I like the film.

It's not just the soundtrack, which has great songs such as 'Mad World' by Gary Jules, 'Love Will Tear Us Apart' by Joy Division and 'Notorious' by Duran Duran, but the score of the film is amazing too. The score is done completely by Michael Andrews, who also plays the piano on 'Mad World'. Just check out 'The Artifact and the Living', which is definitely the standout piece.