all the ones that've been mentioned a thousand times, like vore, piss/shit stuff, gore, furry yadda yadda.
Also the whole loli/shota (I thiiiink that's what it's called but might be wrong) thing, which pretty much equals pedophilia to me, anything with having sex with or otherwise hurting animals

... aaand... hmm... Also, someone mentioned munging, which I then looked up and holy fucking Jesus... :S
Additionally, I once (by accident) discovered that there are some people who are sexually attracted to really veiny women! Like, sick veiny. That creeped me out quite a bit.