I love Bernard Herrmann so much. As cliché as it is to say, his score to Psycho is my favourite movie score of all time. It adds so much that fillm; not only in the famous shower scene, but all the way through, being a constant source of dread and tension and suspense. I could listen to that score completely independently of the film and still really enjoy it. On top of that Herrmann's scores for Vertigo - as mentioned above - and Taxi Driver are really like what Lt. Col. Fantastic says: creepy and kind of beautiful at the same time. That trifecta of scores is probably the greatest in cinema history, if I'm not being too hyperbolic! :P
With regard to more modern film composers, I really like the works of Jon Brion (I <3 Huckabees), Cliff Martinez (Contagion) and Carter Burwell (nearly everything by the Coen brothers, but especially Fargo and Burn After Reading). Burwell is more traditional, despite making some very eccentric and eclectic scores, whereas Brion and Martinez use a lot of electronic software in their scores which have a surprisingly potent effect. The Huckabees score, for example, is ridiculously distinctive one, but it contains instruments that I'd never even heard of until a Wikipedia search informed me of their existence. All this new technology isn't all bad if it's being used for such beautiful music such as this.