IM Weasel seems a bit too childish for me. As does Cow And Chicken. The characters do funny voices all the time, for cheap laughs I guess, IR always sniffs his finger and there's a devil with no pants. They need a squirell.
PPG and Dexter are funny--...I don't know why. They just are.
The only time I remember laughing at PPG was when they spoofed cereal. But Dexter had that one episode that was made by a kid--drawn, spoken, everything. It was funny.