Asteroid mining I think is one of the most interesting initial space industries. Something silly like a single asteroid having metals with current valuations of a million times the global GDP. Obviously you can't sell for that much but asteroid mining could make a lot of commodities become insanely cheap, and that would enable some pretty amazing things here at home, and in space.

Like what if steel were cheaper than plastic? If there was enough of it around to build a bridge between New York and London? If you could build a ship the size of Manhattan and then a city on top of it to roam the oceans? If you could build entire cities in orbit or city-ships that slowly wandered the solar system.