Have any of the cast appeared in other shows (not just their name appearing on a video tape thank you very much), so far i seem to have two appearences on the Simpsons:
1) Bender in the background with Mulder and Scully in that episode where Homer becomes a missionairy (There was also a ironic bit about cutting antimated comedies have to be supported by public donoations or they would be cancelled (it was refering to 'Family Guy' but it still applies.)).
2) the PE crew sitting on the sofa at the beginning of a episode.
I am fully aware that there probably another thread just like this one but i can't be arsed to look for it.