Microgravity environment
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Main article: Weightlessness
A microgravity environment is one where gravity has little or no measurable effect. The only three methods of creating a microgravity environment are to travel far enough into deep space so as to reduce the effect of gravity by attenuation, by falling, and by orbiting a planet. The terms weightlessness and Zero-G refer to this same environment.
The first method is the simplest in conception, but requires you to travel an enormous distance, rendering it most impractical. Even during the missions to the Moon, the astronauts only experienced microgravity because they were orbiting the sun.
The second method is, unfortunately, very common. Also unfortunately, it is difficult to fall for long enough periods of time to do much experimentation or to support any commercial activity. There are also problems involving the stop at the end. However, it is still used as training for astronauts and for some experiments. Drop towers and airplanes (such as used by NASA's Reduced Gravity Research Program, aka the Vomit Comet) provide short term weightlessness.
Unless of course you're orbiting a planet, which is really just falling with sufficient speed that you go all the way around the planet and end up back where you started. This is the environment most people think of, with common examples being the Space Shuttle, ISS, Mir, etc. While this senario is the most suitable for scientific experimentation and commercial exploitation, it is still quite expensive to operate in, mostly due to launch costs.