I've previously talked about the hundred worlds and counting; the eight planets, their moons and all of the big, continent-sized pieces of real estate. Right now, I am crazy to consider all of that as real wealth. It costs too much to get there, to get to the Moon, even. Also, none of the technology for making a living, or even building habitats in which to live, is proven. But it all does count as potential wealth, starting with power.
Certain visionaries have talked about He3 and fusion, which is nice; it gets me excited, but fusion isn't here. Hell, fail-safe fission reactors, of which we've had useable designs for decades, aren't here, so let's calm down about that. Sure, fusion is what we'll need in the outer solar system, but not yet...
Certain other visionaries have talked about solar power satellites, even the possibility of turning lunar regolith directly into photovoltaic cells, on site and in place, without going to the all the trouble of refining and exporting building materials to GEO. That's what I would be trying to start up, right now... because, sadly, the killer app for deploying beamed power is military, and demand is only going to grow.
But, if I could, I'd export momentum from the Moon. Drop a cheap fiber-glass space elevator cable down to the surface from L-1 and start hauling tonnes of soil to drop in towards Earth, each shipment cleverly designed to arrive in time to balance a mass lifted off of the Earth, by a rotovator (http://en.wikipedia.org/wiki/Rotovator_(tether_propulsion)#Rotovators), LEO port (http://www.cloggie.org/esseff/millennial-23.html- 'The Moon Goddess and the Son', while alternate history now, gives me chills...), or hypersonic tether. The LEO port is a magnetic cannon in orbit, as mass-driver to accelerate payloads from Earth, or decelerate payloads falling from the Moon. Either way generates megawatts of power! Hell, if I had a nice Earth-based mass-driver launcher up at one hundred klicks altitude (http://www.spaceagepub.com/pdfs/Powell_2.pdf), I could even catch falling moon-dust to power the operation, and any nearby cities, generating revenue to put my dreams in the black...
Transport, power, and a revenue stream to fund Vinnies' Private Space Program. Now all I need is life support, which is all about the habitats, baby!
In free-fall, plumbing is hard to do, and there are a few health problems that don't matter short-term, but do if you're planning to live and work in space for months and years at a time. Getting out of a gravity well, good; living without gravity, not so much. So we cheat and create artificial gravity or at least use physics to provide a work-around suitable to our needs- spin gravity, centripetal force (http://en.wikipedia.org/wiki/Centripetal_force), or the tendency for mass to remain in motion, and, when force to travel in circles, exert a useful outward force. We'd like nearly 10 meters per second squared, but I imagine that a little less would be okay; between 1.6, of Moon-like levels and 4, for Mercury and Mars. Venus would be ~9 m/s^2.
If our habitat is a spinning space tower, turning end for end, which is 100 meters tall, that's a radius at the outer level of 50 meters. Say three revolutions per minute, velocity of 3*100*pi/60 is ~16 m/s, squared and divided by the radius, ~250/50 is ~5m/s^2. That'll do. A 200 meter tower would have full spin-gravity at the out levels.