Name another cartoon that oozes as much surrealist nostalgia in every frame as Rocko's does.
You just can't get much wackier than Felix the Cat. That series was especially crazy. The original shorts were too but I'm not sure about the 50s series, although I have heard that they're not good.
Pretty much any animation from MTV, especially the shorts that appeared on Liquid Television and Cartoon Sushi, were very surreal in a very '90s way. You just can't imagine anyone making something quite the same nowadays.