Poltergeist! I saw it as a kid as well. That clown doll sneaking up on the little girl was legitimately terrifying. The tree coming through the window scared me for years
The Exorcist - seen it once, brilliant film, but never watching it again
The Omen (the old one) - when he's creeping around the house at the end trying to kidnap Damien. The graveyard with the jackals
Salem's Lot - James Mason slinking around and putting kids in binbags for his vampire master to nom on later. The coffin moving up the van
The Box of Delights - no one seems to remember this one, it's this amazing surreal 1980s BBC kid's serial, but it has some really creepy moments.
Ring / Ringu - have mercy I'm never watching those again
The Soft Mints advert from the early 1990s where everything in the world is sort of lumpy and soft and pillow shaped and the postbox laughs manically as Mr Soft strides past in his horrible pillow world way, drawling 'Mrrrrr Soffttttt' like he's just had a stroke. It freaked me out so much as kid I refused go near postboxes for a while
Edit: right you can all share my pain, I've found that bloody Mr Soft advert and it's just as creepy as I remember:
Mr Softttttt