Marble is easy to use and at the same time a swiss army-knife for maps:
http://de.slideshare.net/marbleglobe/marble-1-6en
describes a few important features. Caching for map data happens on the fly
and is configurable. You can also download whole regions in advance - either
along a user-specified route or a whole chosen area. So Marble is also
perfect for offline-usage. You can also use Marble for GPS tracking, import
KML & GPX files and you can query routes. On the other hand Marble is also
the perfect tool for education since it comes with a dozen ready-made maps
about various topics (and additionally you can download > 30 high-quality
maps about different subjects.
