These are mostly canonical works, but it's also a fairly personal list and should be taken with a grain of salt.
These films will not be to everyone's taste, nor should they be. But they will give a pretty broad sense of the history of the field, offer some cultural literacy in a-g film, and should serve as a good jumping-off point for further exploration.
Organized chronologically. But feel free to dive in anywhere you like.
Many can be found on YouTube, Ubuweb, or other nefarious sources.