For US History and Civil War History, I really like the Civil War Trust. It has detailed lesson plans and resources to help educate students. They also have detailed battle maps, which allow students to see how the battles went. Some of the battles have detailed videos to go with them, leading the students into what actually happened. One of my favorite lessons is the one about John Brown. Our textbook does not go into detail about what he did, but I think it's important for students to understand how his actions affected the war. And this site gives a great lesson plan for it.
This TED Talk really goes in depth in discussing who Genghis Khan was and what he did. They try to figure out if he was a vicious barbarian or a unifier who paved the way for the modern world. It goes into detail about the common (possible) misconceptions about Genghis Khan. By the end, there is no "right or wrong" answer, leaving the audience to come up with their own conclusions. However, I really like how this talk brings up the possible problems with history -- that it is an interpretation of the past -- and that it's told from the winners perspective. How does this affect what we know and learn about?
I've found that feudalism is really difficult to understand for students. So, going through simulations really helps them in understanding the social order and strictness of Japanese feudalism. This simulation is excellent because it really explains what each persons role is and how they are part of the larger picture of feudalism.
This site comes with a scavenger hunt, where students can read about and discover what life was like in ancient Egypt for different social groups: the pharaoh, a nobleman, a farmer, a craftsman, a priest, a soldier, and a woman. It tells an actual story of what each of these people do, from when they wake up until they go to bed. It really helps student understanding when diving into what the social structure of ancient Egypt was like (and why it was that way).
This site is great! It has an interactive feature which allows students to actually go inside the Great Pyramid and look 360-degrees around the pyramid complex. It's really great for getting the students to understand the purpose of the pyramids and why they were built.