In discussing The Day the Earth Stood Still and Herrmann's wonderful orchestral theme, I was reminded of two other musical pieces that create vivid images for me.
The first is The Emperor's Ming's Theme, from the old Flash Gordon movie serial. It was from Franz Liszt's Les Preludes, and whenever Ming the Merciless showed up, the band cranked. Listen to it here, particularly the last section.
And the other is, of course, Vader's Theme, sometimes called The Imperial March, by John Williams. I can't help but think he was trying to evoke the same sense of dark majesty.