A good find by the folks at BoingBoing: Dementia 13, Francis Ford Coppola's slasher/thriller from 1963, can be downloaded for free over at Archive.org. You can watch an embedded version above, or download an AVI file here. Here's the gist of the plot: "An old Irish family is haunted by dark secrets around the death of a little girl seven years earlier. Two women, one married into the family and one soon to be, start unraveling the secrets at a price that they couldn't have imagined." Although Coppola had two prior films under his belt, Dementia 13 is considered his first mainstream, "legitimate" directorial effort.
More great films can be found in our big collection of Free Movies Online.