Keep in mind that these are by no means favorites, just -- per the topic -- the five that I thought were the "most disturbing." In no particular order:
1-) MEN BEHIND THE SUN
2-) SALO: 120 DAYS OF SODOM
3-) ZOMBIE
4-) I SPIT ON YOUR GRAVE
5-) NEKROMANTIK
J.N.
http://members.tripod.com/~NEWMANATOR/index.html