1 - The Changeling - have to agree with CcC here; for me it was the banging on the bathtub that really freaked me out, plus the kid looking up from the well...man that was messed up.
2 - The Ring - Just the girl coming out of the damn TV is enough to make the list - that was seriously freaky.
3 - The Exorcist - All time classic, still does the trick almost 40 years later.
Those are the ones that come to mind right now (probably because they were all mentioned already) but i don't think any movie ever creeped me out as much as The Changeling.
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