In "The Lorelei Signal", Uhura gets to command the ship, and does a great job. Sure, it's only because all the men are incapacitated, but it's still a big step up after the NBC execs refused a script from the original series where it happened because "no one will believe her in command."
"Yesteryear": Young Spock prematurely does the kahs-wan ordeal, and I-Chaya follows him despite his orders. The thing is, I-Chaya is very old for a sehlat, and not really conditioned to deal with long periods of work. Despite this, he follows Young Spock into the desert anyway... and when his master is being threated by a le-matya, he runs up and bowls it over, snarling fiercely. He doesn't last long in the follow-up fight, and sustains a grievous wound, but he lasts long enough for Adult Spock to nerve-pinch the creature's neck.
And in addition, he doesn't show how affected he was by the wound until he has no other choice: when he falls over on his side. THAT's how loyal he is.
In a meta moment of awesome, "Yesteryear" is considered the best animated episode and the only one Roddenberry considered making canon.
"Albatross": Spock comes to break McCoy out of prison. Most people would take that and run, but the good doctor insists on staying until he finds out if he was responsible for a devastating plague on the planet, even if inadvertently. It doesn't last once Spock informs him that the crew are dying of that same plague and need a cure, but it really proves how good the doctor is.
The ending of "The Pirates of Orion." The Enterprise has chased down an Orion ship which stole the medicine that they need for Spock and attacked the freighter crew who were carrying it. The Orions know they're caught, and the captain plans to blow his own ship and the Enterprise to pieces to protect the Orion image of "neutrality." But Kirk has no intention of letting it happen. Yelling to Scotty to activate the transporter, he pins the other captain and holds him until they are beamed up. The Orion captain tries to commit suicide, but two redshirts grab him and prevent it. The Enterprise crew not only saves Spock, but also blows the Orions' cover. Not a bad day for a single starship.