I say this every October we do these threads, and I will still hold to it: the smartest and most efficient horror films in my mind are where your imagination fills in what you're not seeing. No one was better at that than Val Lewton.
By today's standards, they're not scary, but the atmosphere and psychology mostly holds up, unlike a lot of old horror. Cat People, The Body Snatcher, Isle of the Dead, I Walked With A Zombie, Ghost Ship, Bedlam, and his absolute best one, The 7th Victim. Holy shit, The 7th Victim still holds up over 70 years later, what an unnerving film. I didn't include Curse of the Cat People because that's more of a kids film - but if you have a kid, it's perfect for them, and still a good sequel.
Simple scene here, but a prime example of how you can create mood with very little money:
I remember watching the scene in the remake, and minus the beautiful visual of Annette O'Toole, it did nothing for me. Orson Welles was right, every performance looks better in black and white.