Nearterm Habitats and Condos
Inflatable and Expandable Habitats
The first generation of private sector space habitats will be inflatable and launched up from Earth, to be used for private space stations, and for human missions to the Moon and asteroids near Earth.
Lunar and asteroidal materials can provide shielding, as well as supplies of water and other things.
For many decades, the American and Russian space agencies built and launched rigid habitats. In the 1990s, NASA started developing inflatable habitats with its TransHab program. However, budget cuts led to NASA abandoning that.
Bigelow Aerospace took over and has developed, built, tested, and launched inflatable space habitats, starting in 2006 when it launched Genesis 1 on a Russian converted ICBM rocket, and Genesis 2 outfitted with more equipment in 2007. Genesis 1 and 2 are a prototype of size 4.4 x 2.54 meters when inflated and expanded, totaling 11 cubic meters. Both have been a great success, and continues operating and sending data to the time of this writing in 2012, proving the stability of the materials and seals.
Bigelow has been building and will launch a much bigger inflatable -- 330 cubic meters of volume -- in 2013, called the BA330. It will have 4 large windows.
Bigelow calls these "expandable" rather than "inflatable", which makes more sense, but Google still shows an 8:1 ratio of inflatable vs. expandable as of 2012.
These inflatable modules have a standard docking port so that they can be connected to form very large space stations. They will also connect to the International Space Station (ISS) if desired.
A configuration can be rotated to produce artificial gravity by the centrifugal force.
The main advantage of an inflatable space habitat is obviously that it can be packed into a much smaller payload and then greatly expanded after delivery into space.
Testing has shown that inflatable space habitats are actually a lot more resilient against meteor impacts, because there is less shock wave propagation. They also create less secondary radiation.
More can be found about these expandable modules by this link on the Bigelow website.
PERMANENT also has a section covering Bigelow Aerospace as a leading space development company.
Rigid Space Habitats
To date, government space agencies have launched rigid space habitats, such as the International Space Station (ISS).
The Russians have their well proven Salyut space stations, and of course the history with Mir.
There was also some past work into using possibly using fuel tanks as habitats, being that the fuel tanks were much larger than their payloads. In fact, the US Skylab space station of the 1970s was a fuel tank.
There are two types of fuel tank habitat: wet launch vs. dry launch. In a wet launch, the fuel tank is outfitted inside with the floors, walls, and other basic structure before the fuel is loaded, and the payload has the internal fitouts such as computers, chairs, etc. In a dry launch, just another tank is added on top and fit out on the ground, with no fuel in the habitat tank.
Skylab originally considered wet launch but later opted for a simpler dry launch. (After all, it was government and didn't need to be profitable.)
These are all considered near term, first generation space habitats.
Habitats built structurally from lunar and asteroidal materials, needing nothing from Earth, would be considered second generation space habitats.