Thanks, @nathanveshecco! I really loved the theremin. I will add: this was all done from memory. However! I did confirm through Google (made one incorrect assumption listed as an honorable mention).
  1. The Day the Earth Stood Still - definitely the most famous theremin appearance in a film.
  2. "Whole Lotta Love" by none other than THE ZEPP. Less spacey and more ominous and AWESOME.
  3. The theme to the brilliantly campy TV show Dark Shadows.
  4. "Good Vibrations" by the Beach Boys uses an electro-theremin (controlled mechanically, not with one's hands).
  5. Used in "Mysterons" by Portishead, also one of my favorites.
  6. The TV show Hannibal (one of my current favorites, FYI, please watch) features the instrument in a subplot where Hannibal teaches his lover how to play it.
  7. Honorable mention:
  8. The Doctor Who theme. Does not use a theremin, but the instrumentation evokes the same eerie tones to delightful effect!