Riku and Mickey's friendship. Seriously, every scene where they show what good friends they are is adorable.
It was really touched when upon Riku and Sora's return to Destiny Islands at the end of KH2, Mickey passes Sora completely and goes straight for Riku. The joy on Mickey and Riku's faces gave me all kinds of warm, fuzzy feelings. This is to show how far the friendship between these two have been through.
Also, Mickey allows Riku to call him by his first name instead of calling him as "Your Majesty".
Sora, Donald, and Goofy's friendship! They have their fights, but who can forget Donald telling Sora that the Gummi Ship "runs on happy faces" or Goofy protecting Sora from Riku's attack at Hollow Bastion?
Alot of Disney-based moments; that should go without saying!
In any of the games, whenever you complete a 100 Acre Wood level.
The conclusion to Sora's last visit to the Hundred Acre Woods in the first game has him, Pooh, and all their friends looking up at the big, beautiful moon together on a hill, before Sora waves goodbye, and the cover of the book changes to a drawing of Sora holding Pooh's hand as they walk side-by-side.
"Sora, don't forget. We shall always be here. If you'd like to visit again, that is."
In Chain of Memories, once you've found all of Pooh's friends, Sora says he has to get going, and Pooh sadly asks, "Is this goodbye?" Then Sora has a heartwarming smile and says that he'll always visit, before he realizes he may forget all about the Hundred Acre Woods. Pooh reassures Sora that even if he does, Pooh will never forget him.
In Kingdom Hearts II, Pooh unfortunately forgot who Sora was anyways. But at the end, Sora and his animal friends all get together again on that same hill they bonded a long time ago. There's a touching line from Sora that he'll always be in Pooh's heart, and they'll always find each other. Then Sora is off again, and the torn cover of the book restores itself to a drawing of Sora and Pooh looking at the stars together.