I love cartoon expressions that really stretch beyond the characters model sheets in terms of expressions. It helps make the cartoon funny visually.
My favorite part in the Avatar episode, "The Great Divide" has great expressions from Aang:
Some fun ones from, "The Waterbending Master".
Katara looks really badass in this one.
Aang's expression in this episode always made me laugh:
I wish I had pics of Azula. But the DVDs are in another room.
Now Ed, Edd, n Eddy had a lot of great ones:
Now the ones from the movie had some good ones too. I like Ed's serious face, you know he's about to do something awesome when it appears.
Melon Head.
Ed's happy face is always funny:
Never seen Double D so angry.
His fight with Eddy is one of my fav scenes.
Like Lee's expression
I love their expression as Eddy confesses.
This is my favorite expression in Looney Tunes. "Cheese Crackers" has the dog, dumbfounded as the world he knows goes a little awry.
And last but not least, my favorite part from the film Tank Girl:
Because you just don't see enough animated women pulling crazy wild takes.