City On The Edge Of Forever: Spock uses primitive technology to construct a machine to access the information stored in his tricorder. Genius is genius regardless of surroundings...
The Empath: Spock has the flash of insight that his own resistance to the energy field is what is empowering it.
The Galileo Seven: When all hope is lost Spock chooses to bet all on a desperate act, he jettisons all the remaining fuel to signal the Enterprise, knowing having done so within seconds the shuttlecraft will spiral into the atmosphere and burn up
In Galileo Seven Spock also says something like, "I, for one, do not believe in angels," indicating his skepticism about an afterlife. Does that make Spock the first (implicitly) atheistic character on a network TV series?
Hopefully at least one or two would show a virtue of non-straw rationality.
Episode list