A couple of mine

kathy bates sledge hammering feet in misery
spiderwalk from the exorcist
leatherface scaping skin off arms of victim in tcm the begining
leatherface chainsawing through victim balls first in tcm 2003 unrated
hannibal when the guys cuts his face up in small pieces and feeds it to his dog...also when he gets his face eaten by savage pigs

I'm sure there are more i can't think of now

Have you seen the lizard spiderwalk scene? Where she goes after her mother's ankle?

O! you all have already mentioned my favorites...
[1][2][3-5]though I haven't seen any of the Guinea Pig series but I heard there are some very disturbing elements.

Lets see.
1. The rape scene in Irreversable
2. The Animal killings in Canibal Holocaust
3. Most of August Underground Mordum
4. The dog shit eating scene in The Pink Flamingos..........I just dont get it....why????????

I've only seen 1, 2, and 3, and they are absolutely ridiculous. Especially #1. It almost brought a tear to my eye. :o

birthing of alien
birthing of species.
tit removal in cannible ferox
cock removal in above flick.
my avatar

Some random ones I thought were disturbing (not most, but good)

Tom's death in Final Destination

Barb wire fornication in Silent Hill

Dad killing Mom in 28 Weeks Later

1. Fire extinguisher scene in Irreversible.
2. All human experimentation and cruelty scenes in Men Behind the Sun.
3. Hannibal Lecter eating the brain of a live victim, having removed his scalp in Hannibal.
4. Anything August Underground.
5. For pure terror, "that" scene in Woman in Black.

The ending of Hannibal too.

haha that's the scene in the SAW series that bothered me the most too! :p