The terminator, blew my fcuking mind at the time when that steel skeleton emerged from the ashes.
Friday the thirteenth comes a close second, was pretty scary back in the day and happened just as people were getting up to leave the cinema as the calm lake scene filled the screen. It's the only film I've watched where I've seen people hysterical in their seats with fear.
Probably nothing nowadays as it's been done a thousand times over, Carrie was probably the first to do it with the 'hand' scene at the end but I didn't get to watch that in the cinema.