This wins hands down. Scared the bejeebus out of me as a kid.
It's the trailer from the 1978 film "Magic," starring Anthony Hopkins as a ventriloquist with an "evil" dummy. Believe it or not, the film was OK, the dummy wasn't too scary, but the trailer was a whole other story.
Shout out to You Tube for unearthing this scary gem:
http://www.youtube.com/watch?v=nvSw5v3PoFw