I quite like the music in the jam session Spock has with the chick playing the bicycle wheel. I was happy when they released it ("Far Out Jam") as part of the complete recordings box set
The box set is great, alright. I even like the embarrassing rock n roll songs, in private of course.
The girl playing the wheel is Deborah Downey. Along with Charles Napier, she sang her own part. The performance scenes were lip-sync'd to a playback tape, but that's really her singing on it. She went on to become a painter, and one of her commissions was a portrait of Gene Roddenberry.
"Girl #2" was played by Phyllis Douglas, a favorite ST hottie of mine. She was on the show twice and got to ride the shuttlecraft both times. She probably thought they used it in every episode.