USGS (United States Geological Survey) has a great site for educators. There are lesson plans, resources, links, and much more for teachers to use with their students. Topics include Biology, Geography, Water, and much more and are organized by K-6, 7-12 and even undergraduate. You can also search the resources.
There are videos, animations, lectures, maps, pictures, activities, and much more. The quality is very good.
The USGS is also active on social media and invites teachers and students to connect with them that way.