This is too good to leave in comments. A reader named Chris commented on my earlier post about NOAA maps with a list of sources.
Humans generally take in information much faster visually, and retain it longer. Maps provide a key tool for teaching history. The more the better, I think.
The NOAA data center is one of many really neat places to get data, images, and materials. Here are a few more (and let me know if you want more on any one topic, as I collect links like these – and happen to work in the field!):
Earth Observatory Science site. Free! One of the best sites out there.
Find Space Objects! Easy views from your location. Cool.
Elevation, land use, maps, and lots of other GIS data:
Learning technologies. Some fantastic educational materials:
Direct Readout Data. Great images.
Distributed Active Archive Center.
More great free images.