Maybe a versus of Blood Feast versus 2000 Maniacs, or maybe just a single one. I know they're not GOOD movies, but one of them belongs in the canon I believe; A) he did gore in a way that no one ever had before, and sort of broke ground for future, grimier movies, B ) I think it would be interesting to discuss whether a movie that is so clearly exploitation can be in the canon. Both these movies really force the question: are movies works of art, or are they commercial products?
Also I'm pretty sure both of these are watchable on youtube.