NeoK12 has a large selection of educational videos sorted by subject and topic. They’ve all supposedly been reviewed by teachers before posting.

Unfortunately, they all seem to be hosted by sites like YouTube, which mean they can’t be shown in my schools because of content filters. However, NeoK12 might be a good way to identify some good videos that would be useful in your lessons. You could then use one of the methods in The Best Ways To Access Educational YouTube Videos At School list to show them.