I dunno, I don't ever really find films scary. I think seeing things in a busy cinema undoubtedly makes them more enjoyable - I saw Insidious in a sold out show and the film was dross and not terrifying but I found myself jumping a couple of times. On the flipside, The Changeling is meant to be one of the scariest films made but I watched that by myself at home and didn't find it bad at all.
I think mine is probably the Village of the Damned, just because I saw it as a kid and it properly freaked me out. Might rewatch it, bet it's terrible.
Did anyone ever see The Hole 3D, the 'kids' horror? That was freakier than so much out there