It's an obscure choice but I *love* his score for 70s disaster film The Cassandra Crossing. I think the textures, polyrhythms/cross rhythms, instrumentation and mood are just incredible - the film is about a virus spreading on a train across Europe and somehow he manages to combine a sonic evocation of both things, the clanging, metallic chug of the train together with the feverish claustrophobia of the sickness. The main theme is beautiful and mysterious but the action cues are something else, their climactic moments are genius... It's a shame the film itself is kind of forgotten as a footnote to the disaster movie boom as the score doesn't get the credit it otherwise might. 14:12 in the video below is a good example to start with in this score:
Of course I also love Alien, Poltergeist, Chinatown (even though LA Confidential is the better score I prefer the Chinatown theme), Papillon, Logan's Run...