Here are some random facial expressions from the Ren & Stimpy episode "Insomniac Ren", directed by Steve Loter. Even after John K. left, there were still funny drawings present, despite what the Games haters would have you believe. Though I'll concede that the art style got flatter.
Handsome faces like these two always make me laugh. They're just so chiseled and serious looking that it seems ridiculous on the short, exagerrated bodies of cartoon characters.
Classic Simpsons experimented with the characters animations a lot more than they do now. Some of them were just so over the top they stand out in every episode they're featured.
I like to think of the SpongeBob series as the king of reaction faces. I don't think it's possible to look at any of these and not smile a bit.
Here's a few misc. ones from The Marvelous Misadventures of Flapjack:
And all of these came from one episode, "K'nuckles and His Hilarious Problem"
(I do not find this episode hilarious at all, but still one of my favorites)
It interests me how Flapjack can contrast itself so much,
mixing in adorable faces and moments like the last picture,
and then shoving grotesque and creepy images into your face that you know you'll see again in nightmares.
All of these are funny (or in the case of the Stimpy's Cartoon Show pic, emotional) expressions that can potentially be enjoyed even if you don't know the context of the scene.
You know, for a kids show, a show meant for girls and a magical girl show, the Ojamajo Doremi has had some of the most freaky facial expressions. Almost One Piece level, even.
Uh-oh. 3 of them are bored, except Mugi, who seems to do the blank white eyes for no reason.
It looks like Kisaragi ate too many...chocolate beans or something.
Rika and Satoko look like they're in a buddy cop movie.
This is Coraline's "meh" face. For some reason, this makes me laugh.