Mo Willems is the creator of "Sheep in the Big City", and the head writer for the first four seasons of "Codename: Kids Next Door". While the premise for Codename: KND doesn't appeal to me, Sheep is one of my favorite cartoons. I won't go deep into it, because you could easily read my review for that show, but I will say here that it is without a doubt one of the smartest, funniest cartoons I've ever watched.
Along with Sheep, I also liked "The Off-Beats", an animated set of shorts that used to come on between shows on Nickelodeon. It isn't an extreme favorite of mine, but they had some nice little shorts.
Mo Willems is also the writer of a few children's books, although I have never seen or read any of them.