Jerry Goldsmith's musical score, which invented the Blaster Beam (if you saw Inception, you know what it is).
In fact, quite a few of the musical cues in this film would go on to become Star Trek staples. The "Klingon Battle Theme" from the start would go on to become the primary Klingon theme, several of the major musical cues would be referenced again and again in later works... and oh yeah, the main theme to the movie became the theme song for Star Trek: The Next Generation.
The film score received an Oscar nomination, and one of the most beautiful pieces from the film, "Ilia's Theme", is all but forgotten by most non-Trek fans.
The soundtrack of Star Trek: First Contact, which Goldsmith also scored, contains what might have been either a Brick Joke, Mythology Gag, or even unrealized Foreshadowing at the end of the main title: the moment that the Borg Cube appears on screen, the same harsh chord that is played over establishing shots of V'Ger can be heard.