Just another place to find an occasional movie:
Feature Films at the Internet Archive(Especially the
sci-fi/horror section.)
These are public domain movies which means mostly ones that lost or didn't claim copyright before the law was revised to give automatic coverage ("Night of the Living Dead" is a particularly famous example that lost copyright this way). So they're pretty exclusively pre-70s, but if you enjoy corny old sci-fi/horror movies, there's some fun ones here (as well as some old Vincent Price classics and such that aren't half bad). Although, the copyright status of some of them may need to be verified... (I think it's just as claimed by the uploader, but I know some of them are kosher, so willing to give it the benefit of the doubt).
Some examples: "Night of the Living Dead" (of course), "Plan 9 From Outer Space", "Invasion Of The Bee Girls", "The Last Man On Earth" (original version of "Omega Man" starring Vincent Price"), "Manos Hands Of Fate"
Another way to sum it up might be to describe it as the entire source library used for MST3K.
Of course, because they're public domain, many can already be found on Hulu or NetFlix streaming, but not all of them.