Explore world stats using StatPlanet World Bank, the first prize winner of the World Bank's Apps for Development competition. It directly accesses and visualizes all of the World Bank's 3000+ indicators available through its Open Data initiative, on many different topics from Agriculture to Science & Technology. This is a great way to introduce students to thematic mapping and offers incredible freedom to explore what you find interesting. This is the type of resource that could be used for any unit.
Via Seth Dixon