It's basically all there in the title.
As I've mentioned, I'm starting to show my 8 year old a slew of classic films, and I've included Star Trek 2-4 & 6 on that list.
But before he sees Star Trek II (SPOILERS and the death of Spock) I wanted him to see some classic Original Series episodes. Space Seed is definitely on the list. Also the Trouble with Tribbles.
Though I'm drawing a blank on 3-4 other episodes that would be enjoyable for an 8 year old and also establish all of the relationships to prepare him to enjoy the movies.
Help?