I forgot to mention Darmok (TNG). One of my favorite ST episodes, and I'll never forget the time that a philosophy professor showed this entire episode to a lecture hall full of people to make some point about communication or some such.
Would love "City on the Edge of Tomorrow". Bones ODs, and Spock and Kirk go to the late 30's. Really cool.
The other one is also time related. Don't remember the name. T'Pal and 2 crewmates get marroned on 40's or 50's Earth. One ends up staying. Was actually a god view that Vulcans can have different emotional states.