One of those free packages that always seems to be getting better and better. GeoMapApp is “an earth science exploration and visualization application that is continually being expanded as part of the Marine Geoscience Data System (MGDS) at the Lamont-Doherty Earth Observatory of Columbia University.” Great for earth systems science, satellite imagery from many diverse platforms. The Profile tool is handy for explaining DEMs through different visual perspectives. Can be a quick complementary tool combined with other raster-based exercises.
Their educational resource collection has expanded too.