When I think of exquisite sound design, two of my favorite movies spring to mind: Stalker (1979) and The Good, The Bad, and The Ugly.
The former has such a subtle soundtrack that it’s almost like it’s not there, but without it so much of the atmosphere of a movie that is heavily atmospheric would be lost.
The latter is just a perfect western with a perfect western soundtrack. The theme is well known, but L’estasi Dell’oro gives me chills every time it starts playing.
Beyond The Black Rainbow - A psychedelic loveletter to the 80s, about a dying cult and its first and last victims.
Anything by David Lynch, but particularly Mullholland Drive and Twin Peaks.
Mullholland Drive is a dream logic trip through Los Angeles as a small town actress finds work and love and heartbreak and murder in the big city while the world becomes increasingly incomprehensible and nightmarishly surreal; it also includes one of the best acted, directed, shot and scored scenes in all of horror.
Twin Peaks is the story of a small town deep in the forests of Washington, struggling to solve the murder of a high schooler, an FBI agent arrives and proceeds to explore esoteric and supernatural causes; part drama, part cosmic horror.