There are thousands of film at the Prelinger Archives, free to use.
They are movies where the copyright is outdated and therefore belongs to the public domain. This means that they are rather old and the format is less favorable than today's but never the less they are there and free to use.
There are both documentaries, things used in newscasts and such, and a variety of fiction films, some animated.
One favorite is this one about a toy truck.