Specifically, the incidental music from an episode of The Original Series. More specifically, the episode Metamorphosis.
If you've never seen this particular episode, I can't recommend it highly enough; I consider it Star Trek at its best. In the episode a mysterious energy field takes over a shuttlecraft on which Captain Kirk, Mr. Spock, and Dr. McCoy are en route back to the Enterprise after picking up an ambassador named Nancy Hedford, because the ambassador has contracted a rare disease and has to receive treatment. The energy field diverts the shuttle to an uncharted planet which is home to a single human man, and it turns out that this man is Zefram Cochrane, inventor of the warp drive and a man who should be dead because he lived something like two hundred years prior to the episode. We learn that he was brought to this planet by that energy field, and that the field has brought Kirk, Spock, McCoy, and the ambassador there to provide Cochrane with companionship.
After some ill-fated attempts at escape, Kirk and company realize that the energy field (which Cochrane calls "The Companion") is actually female (keep in mind, this show was written by 1960s views on gender roles) and considers itself Cochrane's lover. They try to convince The Companion to let them go, with Kirk pointing out that since Cochrane and the Companion are different species, they can never truly love. The Companion merges with Ambassador Hedford, curing her disease and thus becoming human, and as Kirk and company depart, Cochrane and Hedford/the Companion are settling in for a lifetime together.
Setting aside the 1960s notions of love and gender, Metamorphosis is one of the finest science fiction love stories I know, relying on insight and discussion over phasers and fistfights. It also boasts a deeply lovely and finely textured music score by George Duning which highlights the otherworldly nature of the beings involved and the hesitant wonder of their first steps into the world of love. This suite was apparently edited together by someone with good sound processing abilities, even if they weren't entirely able to isolate the music from the occasional sound effects of the show. Enjoy!