British Pathe, which documented the first 70 years of the 20th century in cinema newsreels, has uploaded its entire 85, 000 films to YouTube. Altogether that's just over 3,500 hours of footage! The news reels range from the sublime (like the Wright Brothers First Flight) to the ridiculous (like the Chain Smoking Chimp).
This is an invaluable resource as it does have some fascinating video, I've selected a few that I thought could be useful for teaching but obviously I have only scratched the surface. Enjoy!