Sparx's status as Chiro's Cool Big Bro, complete with Affectionate Nickname. It's been pointed out that Sparx is initially the best at handling Chiro when he's scared or upset, which anyone can tell you are the times you need support and sympathy the most.
Pretty much everything pertaining to Sprx and Nova in "Wormhole" and "Belly of the Beast".
In "Skeleton King", after Chiro rescues the monkeys:
Nova:(hugging Chiro) Chiro! I don't think you know how glad we are to see you.
Chiro: Believe me, I do.
After being manipulated by the Skeleton King, Planetoid Q decides to make its own choices and its first is to become like the Monkey Team by morphing into a giant Monkey Head and traveling the universe acting as a protector. The Monkey Team now has their very own Mogo.
Nova:(practically tackles Antauri with a hug) It's you! It really is you!
The following exchange between Chiro and Antauri shortly after that is just as adorable.
Chiro: I knew you were never gone!
Antauri: I was always with you. Within you, Chiro. I owe you my life.
Nova glomping Gibson after he saves everyone in "Invasion of the Vreen" was quite sweet.
Sprx apologizing to Nova for throwing the snowball at her face in "Snowbound" was quite considerate of him. He even tries cheering her up by making a funny face after she remarks that he's "the dumb monkey" in an almost affectionate tone.
If the mere sight of the Monkey Team as babies in "Golden Age" doesn't cause a squee overload, the way they interact with each other and their human caretakers will. Sprx and Nova play fight, Gibson brings the Alchemist a chip for the Silver Monkey and plays with his tail, and all but Mandarin huddle together in fear. Later Nova sits on the Alchemist's shoulder as he builds her robotic fists, and Antauri runs in fear to hug Captain Shuggazoom. Awwww!
"Galactic Smash: Game Over" has Gibson of all people hugging Otto after being rescued by him, followed by the entire monkey team (save a hovering but visibly overjoyed Antauri) tacklehugging him after his Disney Death.
Sprx and Gibson's relationship. Sure they bicker and tease each other from time to time, but do care about each other.
An example would be "Belly of the Beast", when Gibson was knocked unconscious after Skeleton King robot shocked and threw him against the wall, Sprx cried out Gibson name in worried and attack the robot. Even helping Gibson getting up when he woke up.
In "Wonder Fun Meat World" Sprx cried out Gibson's name in worried when he was attacked by the meat monster Otto coughed up.