Here's two commercials, both public service announcements, that scared countless innocent children of the seventies.
"Sensible children? I have no power over them!" whispers the Grim Reaper. One wonders how many poor kids literally died of fright after watching this PSA called "Dark and Lonely Water".
This Hanna Barbera anti-drug PSA actually makes me want to drop acid. The groovy music, the rainbows, the undead behind the door...
Can you imagine some poor kid in his footy pajamas watching The New Zoo Revue suddenly being confronted with this psychedelic horror-show?
I don't personally have a recollection of this PSA from childhood. Although, considering its horrifying nature, I may have repressed it. It was brought to my attention a while back at The Lazy World of Arthur Ignatowski (the sort of place you're likely to find long forgotten gems like this).
If dark and disturbing public service announcements are your cup of tea, I recommend you visit Scare 'Em Straight on TV Tropes Wiki, where these disturbing Saturday Morning PSA's and those blood-soaked gorefests called Driver's Ed films are explored in detail.