Spongebob is hee-larious.

I know this may sound dumb, but there is this new show on Nickelodeon these days called Avatar: The Last Airbender that is simply badass. It's an anime-esque cartoon with an interesting story and phenomenal characters. The animation is well done, but the range of characters and the way that it conveys their emotions is top-notch.

Though the 'toon is obviously for older children than 2-5 (I'd say for 8-13 year olds), it is certainly among the calibur of Spongebob.