My scariest PG rated movie is definitely The Haunting. Psychological horror at its best. As a kid I shit my pants watching Poltergeist, that was quite something. And as of late Dead Silence and the awesome Insidious.
I don't think it was the scariest movie, but quite a few scenes in Insidious scared the crap out of me. The man pacing out of the window, the screaming on the baby monitor, the person behind the crib, Darth Maul behind the guy's head, the creepy little person.
"It's not the end of the world, it's just the end of the day."