i've mentioned this one before but. . . one of my favorite books about horror films talks about exactly this question. the book is titled Projected Fears and the list of most "influential" horror films in american history is:
Dracula (1931)
The Thing (1951)
Psycho (1960)
Night of the Living Dead (1968)
The Exorcist (1973) & Texas Chainsaw Massacre (1974 - the book actually talks about these two together)
Halloween (1978)
Silence of the Lambs (1991)
Scream (1996)
and, The Sixth Sense (1999)
it wouldnt' have been my list, but the book makes a very compelling case for each.
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Winner HDC Battle Royale I & HDC Battle Royale IV

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