Two sequences heavily reliant on the music, in a sublime way, are; Gillian's Escape from THE FURY (John Williams) Grand Central from CARLITO'S WAY (Patrick Doyle)
AGUIRRE - POPOL VUH : the opening sequence LAST OF THE MOHICANS - TREVOR JONES & RANDY EDELMAN : the final chase in the mountains SEVEN - BACH : Sommerset doing his research in the library LORD OF THE RINGS THE RETURN OF THE KING - SHORE : Lighting of the beacons DA VINCI CODE - ZIMMER : the final sequence at the Pyramide du louvres THE MISSION - MORRICONE : De Niro character Redemption sequence
"The end of TO KILL A MOCKINGBIRD when Scout is on the Radley's porch and knows what it is to stand in another man's shoes. Kim Stanley's voice and Bernstein's music are transcendent."
Great as that is, I think the penultimate cue is even more moving, when Atticus introduces Scout to Boo face to face.
Obviously, most posters here have ignored the instruction to pick just one cue, but I'll try to stick to the rules. That MOCKINGBIRD cue would have been my pick, had it not been for the existence of the one that is, the supreme moment in Walter Schumann's THE NIGHT OF THE HUNTER when Preacher's scream as the river whisks the children's skiff out of his reach melds with the music and echoes in the suddenly still, starlit sky, which is then joined by the little girl's "Pretty Fly" song to her doll.