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Psycho (1960) doesn't count. If it did, that would probably be everyone's favorite.
Mine would have to be Frenzy (1972) about the neck-tie murders.
Runner-Ups:
Shadow of a Doubt (1943)
Rear Window (1954)
I just watched Strangers On a Train (1951) over the weekend. It was pretty good too.
What about you? What's your favorite Hitchcock movie, besides Psycho?