Found this adorable image from a thread over on the Comic Geek Speak message boards. You can see lots of superhero and science fiction characters in the Simpsons house style over at this page on io9. (Sorry, no Martian Manhunter. Or Green Arrow. But we do get two Aquamans.)
I can't get over how awesome Hawkman looks depicted ala Matt Groening. Even the helmet and mace look great.