Classics: The Texas Chainsaw Massacre, Alien, Scream, The Fly, The Shining, The Excorcist, Hellraiser, and of course the big 3 slashers OP mentioned (Halloween, A Nightmare On Elm Street, Friday the 13th).
More recent: 28 Days Later, Let The Right One In, A Quiet Place, Midsommar.
Some others I enjoy: Dawn of the Dead, Psycho, Silence of the Lambs, Blair Witch Project, Paranormal Activity, The Ring, I Know What You Did Last Summer, Night of The Living Dead, Strangers, Final Destination, Poltergeist, Hostel, Tremmors, Cube, American Psycho, The Mist, Ichi The Killer.
(Sorry for the long list. Not everything is great, but crappy/cheesy horror can be awesome too).