There are many nice documentaries on YouTube about science, nature, space, history, etc.

Documentaries on YouTube

• Seeker, Real Stories, DW Documentary, DOCUMENTARY TUBE, Best Documentary, Free Documentary, ADVEXON TV, HBODocs, BBC Documentaries – BBC

Science

• Discovery, Science Channel

Nature

• National Geographic, BBC Earth, Animal Planet, BBC Earth Lab, BBC Earth Unplugged

Space and Universe

• Space & The Universe HD

History

• Timeline – World History Documentaries

Movies

• CineFix