I would agree with Event Horizon. I was 20 when I saw it and had been watching scary movie for years, but there was something about this film that really freaked me out. It is a skillfully created film with just the right amount of shock and genuine scares, and the visuals are perfectly done. I am glad it never suffered any sequels. Also, the final moments of Blair Witch (in the cellar) chilled me to the bone.