The asteroid belt, with robots. There's roughly a planet worth of raw materials, 24/7 solar energy. We just need to supply the labor force. We can collect, manufacture and deliver whatever we need to earth, or earth orbit in the case of spaceships, space stations and immense solar power arrays feeding clean power to those of us down here in the gravity well.
We need to perfect robotic exploration, mining, and manufacturing. We can use the moon as a first step. I say let's go back to the moon when there's a fully functional and pressurized moon base and fuel depot waiting for us on the surface. Heck, we can build and launch a craft to deliver most of the fuel for the trip from there and have it waiting for us in Earth orbit.
The fact that humans are stronger, smarter, more flexible, etc is the reason to do robotics missions -- robotics is the field which needs the scientific development. Robotics is the field where we need a new Manhattan Project. Robotic space exploration, mining, and manufacturing. The moon, and moreso the asteroid belt contains all the raw materials we will ever need (not to mention enough precious metals to completely crash the market for them). The sun provides 24 hour solar energy in space, not to mention there are probably uranium bearing asteroids, and the nuclear waste can be dropped into the sun or safely dumped on a cold rock in the middle of nowhere. Sufficiently advanced robotics which could mine the materials and build the fabs to replicate more smart robots, you've got unlimited labor. So what could we accomplish with unlimited labor, energy and raw materials? What couldn't we accomplish?
Anyway, all that is not going to happen overnight, but I say we develop advanced robotic missions to the moon, and go back in person once we have a fully functional robot-built moon base with life support systems and a big tank of rocket fuel standing by for the return trip. Everything we need to make that happen is up there, some assembly required.
Anyway, the result is a 3 tuner DVR/HTPC with probably the slickest remote driven interface on the market, records protected high def content 3 channels at a time, has no monthly subscription fee, connects to my theater system with a single HDMI cable, plays Netflix (though I do this in the browser -- the WMC Netflix plugin has annoying frame judder), has full web browsing, runs Steam, etc. It works great, and is better in every way than my Comcast box ever was. It really wasn't even that difficult to set up, had I purchased a premade PC with Windows 7 it would have been almost trivial.
We will have solar energy as soon as the utility companies solve one technical problem -- how to run a sunbeam through a meter.