My pick is Stanley Kubrick's 1968 masterpiece, 2001: A Space Odyssey.

Also Sprach Zarathustra by Richard Strauss will forever be one of cinema's greatest opening themes. And combined with the opening credits of the movie with the sun rising slowly over the Earth was absolutely groundbreaking and legendary. It is truly one of the greatest opening credits sequences of all time.

Plup fiction's intro was captivating.

Terminator 2: Judgment day

Hunt for the Red October

The overture for Star Trek the motion picture. That’s right. It had an overture.

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One I didn't see mentioned yet: reservoir dogs.

All of these are good answers, but the movie with the best opening theme is obviously Alan Partridge - Alpha Papa.

There can be only one: Highlander