Movie: The ending part of The Ring when the girl crawls out of the TV. I freaked out at that part considering most of the movie wasn't that scary to me. Just that end part. Mainly because I thought it was over, but then that twist changed my perspective on it. Also the part in The Grudge where the girl is hiding under the blanket.
Supernatural: In the episode Family Remains, the girl who they all thought was a ghost, but was really just a feral kid. To think that she crossed the salt line and nothing happened to her.