I've found this animated atlas useful for when I'm introducing a new unit to show the students the "grand sweep" of history. It's Euroasian-centric and some of the details are wrong, but the students seem to benefit from such a visual display.
Contains historical sources and images as well as geographic and anthropologic information on all the regions of the world. The search function is tailored more for someone interested in anthropology, however the results contain many historical sources.
We got a student subscription to this for our department (which students can access at home as well with their own login) for Aus$200. Money well spent we think!
What an excellent resource! It has a funky interactive map with little information windows that pop up as you mouse over them, and then if you click it gives you more detailed information. Definitely useful for student research or a classroom activity. The maps are quite beautiful.
These are a comprehensive set of pretty-good-quality maps covering just about every decade in Europe since the early C16th. They have some accompanying information which seems reliable enough.