The Exorcist - caught up with this one in an old creaky house that was in the middle of a large orchard! Yeah the effects haven't aged well but the general tone and atmosphere got me!
The Ring - Not sure why, can watch both The Ring and Ring movies without issue now but was unnerved by first viewing. Strangely didn't have the same issue with Ju-On.
Paranormal Activity - packed Aussie cinema, chicks screaming, people running out of the cinema, hell yeah it was awesome!
predator_silver, PA 3 is worth a look, haven't caught the fourth one yet.