Molly wrote George a letter to apologize for all of bullying that she and the Tough Customers did to him in the sixteen years since his introduction. George finally caught a break.
Dr. Fugue tells Arthur's class to perform in the diner they're stuck at instead of the concert that they were preparing for. When they ask why, he says that they worked too hard not to hear how good they sound.
The entire town pulling together to make it through the blizzard.
Any moment where Arthur and D.W. act like loving siblings to each other. For all their sniping and arguing with each other, we see plenty of evidence that they genuinely care about each other.
"Arthur and the Crunch Cereal Contest", when Arthur enters D.W.'s song into a contest he wanted to win. Arthur gives D.W. full credit, and she wins.
A special mention should go to one of the newer intros, in which Arthur spent the entire segment with D.W., helping with her little ritual of naming a new stuffed animal she got without complaining. He actually seemed to enjoy it.
For most of "Lost!", D.W.'s distress at the possibility that Arthur is gone forever comes across as her typical drama queen histrionics, but when he finally returns home, the episode's final scene makes it clear that she was truly worried about him and would miss him if he were to disappear.
(Arthur is about to fall asleep when a bright light suddenly shines from his bedroom door) Arthur: Huh? What's going on? (he sees D.W. standing at the door with a flashlight, which she then turns off) D.W., what are you doing? D.W.: I'm making sure you're not lost. Arthur, you scared me. (climbs into bed alongside Arthur) You'd better promise never to get lost again. Arthur:(moving over to make room for D.W.) Okay. I won't. D.W.: Do you promise?... Arthur: I promise. D.W.: Cross your heart?... Arthur:(sleepily) Cross my heart... (he nods off; D.W. smiles, rolls over, and falls asleep)
"D.W.'s Time Trouble". After spending the episode dreaming about what life would be like if she were the first born child, D.W. wakes up realizing that she prefers Arthur the way he is as he comes in to give her the toys she left in his room. D.W. then tells Arthur that she's glad he's her big brother as she gets into bed with him.
There's another heartwarming scene early on. During the dream, DW convinces her parents to take her baby version instead of Arthur. After travelling into the future and seeing her parents have decided not to have any more children, she feels sorry for Arthur, and leaves him on her parents doorstep so that he can have a family. Even in a dream, she loves him too much to be without him.
In "Never, Never, Never", after the Tibbles have tricked D.W. into giving them her old toys with false claims of love only to begin destroying them, she tries unsuccessfully to get them back. Arthur then enters the Tibbles' house to try his luck, and we hear sounds of a scuffle inside, until eventually Arthur emerges with a box of toys and a broken earpiece on his glasses. During the scuffle, Nadine tells D.W. that Arthur's bravery on her behalf in the face of the twin terrors shows that he really does love her. D.W. decides to repay Arthur's kindness by selling some of her toys to help raise money to fix his glasses.
Dave Read: "Spanky, I'll always remember the time you got loose in my kitchen, and you didn't eat a single poppyseed. Thanks." Coming from a caterer, that's huge.
After everything neat that Buster has seen and done on his trip with his father, the first thing that he wants to do when he gets home is play checkers with Arthur. They pick up right where they had left off.
In "The Great McGrady", Mrs. McGrady is about to clean up a mess that D.W. accidentally spills while she, Arthur and Muffy are visiting. Upon noticing that the cancer has made Mrs. McGrady rather weak, Muffy, of all people, immediately stands up and offers to clean it up herself. Talk about Spoiled Sweet!
The episode where Arthur cuts his knee on a tin can lid while finding a wheel in the junkyard for his school project, where D.W. and Brain show genuine concern for his well-being.