Helium-3, Bigelow claims. Oh, lots of people claim it. Every time someone asks, "What's really valuable on the Moon?", the cry goes up for Helium-3. It's actually worth a lot of money because we don't have much of it left on Earth. We obtained it in the past mostly by detonating nuclear bombs, and we don't do that much any more. But what we use it for is mostly experimenting with what we could use it for.
The theory is that we could use it to create cleaner fusion-based nuclear plants. How realistic is this? Scientific opinion varies widely. The University of Wisconsin is ready to start mining now, even though the fusion-based Helium-3 plant hasn't been invented yet. NASA takes a more conservative view, noting that "tens of millions of kilograms of regolith must be mined to obtain one kilogram of He-3" and "Of course, this story depends on the successful demonstration that the He-3 reactor will work." The real cynics are over at the fabulous science literacy blog Depleted Cranium, whose author states baldly "Helium-3 from the Moon is not going to solve our energy problems."
Okay, so Helium-3 is a little premature. What else is up there? Metals, right? Every headline after LCROSS slammed into the Earth announced "Water and Gold found on Moon!" This PBS article is laid back in comparison, holding off on announcing gold until the first sentence. But none of the articles explain anything. How much gold? How did it get there? By the way, if you Google "Gold on the Moon," you'll get a lot of crazy links that will remind Futurama fans of this episode. (You'll also learn about astronomer Thomas Gold, though, who first predicted that the Moon would be covered in dust, which balances out the Nazi Gold Hidden on the Moon insanity.)
The closest I could come to figuring out how gold got on the Moon was this blurb from Astronomy Cafe stating that meterorites containing gold slam into the Moon, but it seems like we might as well just get the gold directly from the meterorites somehow.
So, no gold miners on the Moon. However, I have to say that I started researching this subject with a huge dose of skepticism and ended up revising my opinion on lunar mining. I don't think it will be gold or Helium-3, but we'll be up there and we'll be mining. My bet is that we'll go after titanium, which is plentiful on the Moon, and we'll also mine oxygen and hydrogen to keep lunar colonies supplied with water and air. I really hope I get to find out in my lifetime if my guess is right.