For me, it's the scene in Horror of Dracula where the vampire gal bites Harker, there a growl, and suddenly the screen is filled with Dracula's face, complete with bloodshot eyes and sharp fangs. Made me jump and I've noticed that scene has made others jump through the years.
Joe "Renfield" Meadows
HORROR-WOOD Webzine
http://www.horror-wood.com