If you are wanting to add supplement videos to serve as a resource for your class (traditional or online),depending on the courses and content matter you teach, many networks offer their TV episodes and videos (or portions of them) online for a limited time.
Also, did you know that YouTube has full length movies and documentaries? Again, how long they will be offered will vary, but it may be worth looking into.
And if you are looking for more free documentaries, here is just another site:
TED.com has some amazing presentations by people all over the world on various topics as well that could be great discussion starters for a class.