Helium-3 is a rare earth mineral in gaseous form with the potential to fuel clean nuclear fusion power plants. While scarce on our planet, He-3 is extremely abundant on the moon. A single load of the US Space-Shuttle is contended to power the entire United States for one year. Therefore, NASA plans to operate a permanent base on the Moon by 2024, but also China, India, the European Space Agency ESA, and at least one large Russian corporation, Energia, have plans of setting up manned lunar bases that should be in operation after 2020.
I find this video about He-3 very informative and to-the-point. Christopher Barnatt discusses the nuclear physics of fusion, space exploration and the global politics that may be involved in mining space for helium-3.