The space elevator

A space elevator is a proposed megastructure designed to transport material from a celestial body's surface into space. The term most often refers to a structure that reaches from the surface of the Earth to geosynchronous orbit (GSO) and a counter-mass beyond.
Current technology does not make available, in engineering quantities, materials that are sufficiently strong and light to build a space elevator for the most interesting case, from the Earth's surface to GSO. The Earth's effective gravitational potential well is simply too deep. However, the total mass of material needed to construct such a structure is an extremely strong function (exponential) of the strength and density of the supporting cable material. Carbon nanotubes appear to be interestingly close to making this possibility practical. Recent proposals for a space elevator are notable in their plans to incorporate carbon nanotubes into the tether design, thus providing a link between space exploration and nanotechnology. Because the Moon's gravitational potential well is approximately 20 times less deep than Earth's, a lunar cable, over the Earth-Moon Lagrangian point, L1, appears to be feasible even with current commercial materials, and could revolutionize the economics of the space use of lunar materials.
Despite all the daunting problems that face them, the space elevator enthusiasts say with research, time and money, they'll find a solution.
They insist that one day there will be lots of elevators ferrying satellites, prospectors and even tourists into space. They say the benefits of having them in space will be worth all the efforts.
Right now the cost of getting into space is one of the major blocks to more exploration. Mervyn Kellum has done studies on the cost of transportation comparing rockets to the space elevator.
Further reading :
http://en.wikipedia.org/wiki/Space_elevator
http://www.cbc.ca/news/background/space/spaceelevator.html