Prolly waaay too late to contribute to this but we missed several major contenders:
Bride of Frankenstein (an amazingly layered allegorical horror piece)
Cat People (a Freudian maelstrom...more psychiatric monographs have been
written about this movie than any other)
Island of Lost Souls (wow....hard to describe....truly weird Laughton)
Freaks (like no other movie ever made)
Nosferatu
Twin Peaks (the series, not the chopped up 2 hour movie)
Cell, The (pure evil, unforgettable visuals)
Invasion of the Body Snatchers (found usually in Sci-Fi, really political horror)
and....
The third story in Karen Black's "Trilogy of Terror"...the one with the tiny African cannibal fetish chasing her around her apartment) All you women out there that saw this know what I'm talking about, heheheh.... Yikes!
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Beyond that, what are the rules to this ladder... how does one vote for each level?