For me, it was Hush...Hush, Sweet Charlotte (1964), one scene in particular. After Charlotte (Bette Davis) accidentally kills her doctor (Joseph Cotton), her cousin Miriam (Olivia de Havilland) helps her dump the body into a swamp. Returning back to the spooky southern bayou mansion, Miriam goes to park the car while the traumatized Charlotte goes inside and begins crawling up the grand staircase on her hands and knees when she notices wet footprints on the steps. Looking up, she sees the mud and swampweed covered putrescent corpse of Dr. Bayliss standing over her, a ghoulish grin on his pallid face as he extends his hand down to her. And, of course, the soundtrack music added the perfect touch. My blood ran cold.
There were many other '60's films that chilled the body temperature right out of me (Curse of the Living Corpse was one), but that one I particularly remember.
Gerard