Star Trek II: The Wrath of Khan
Star Trek II needs no futile word from me to give voice to its genius. The best of the original films by a mile and a half, Wrath of Khan was a virtual franchise unto itself. If you are unfamiliar with anything Star Trek, watch the Space Seed episode of the original series and then watch this film. After you have been immersed in its boldness, intelligence, and raw entertainment value, go back and watch J.J. Abraham's remake again. So much of what made the remake great was its borrowing from Star Trek II so it provides an interesting compendium piece.
The reason this is on my list is because lately I have taken to watching it as I drift off to sleep. Star Trek II features one of James Horner's many, if overtly similar, scores that never fails to delight me. It's like the perfect geeky lullaby and I'm usually out by the commencement of the Kobayashi Maru. What's really fun is, should my sleep prove restless, fading in and out of the film at different points. It's like watching a very strange fan edit of the film that somehow involves Kirstie Alley's hairdo leading to the discovery that Kirk has a son, or Scotty's wee bout of shore leave causing Kirk to exclaim, "Khannnnn!!!" Still a great film no matter how much you sleep through.