The science fiction movie Moon
presented the idea of mining an isotope of helium (called He-3) from the soil of the moon and shipping it to earth for use in nuclear fusion reactions, to produce commercial electricity and thereby solve the global energy problems of our planet.
He-3 exists in abundance on the moon but is almost non-existent on the earth. It is present in the lunar topsoil. In principle, one merely has to scoop it up, process it, and ship it to the earth, all of which is quite cheap (the expensive part would be getting the equipment and facilities to the moon and setting up shop, the actual "mining" and shipping costs are negligible).
Setting aside the question of a practical fusion reactor (more energy out, than what goes in), and skipping the advantages of He fusion versus Hydrogen fusion (He fusion is much cleaner than Hydrogen), here is a brief analysis of how much He-3 would be needed to supply the electrical needs of the US (in 2007):
Click to enlarge: