An effective but seldom-used device that made a big impression on me was the use of major thirds moving chromatically up and down beneath a melody. This results in some unsettling harmonic ambiguities, particular with regard to the augmented chords that are formed along the way.
I am going to post three representative examples.
Kenyon Hopkins uses this device more than anyone else I've encountered, across many of his albums and soundtracks. You can hear it in his version of “Spellbound” at the 10 second mark:
Elmer Bernstein uses it in this track from the Staccato soundtrack album:
And finally, Nino Rota uses it at the 0:33 mark in this track from La Dolce Vita:
This sound brings to mind the eerie blueish glow of a B&W TV set late at night, with all the other lights off.