One of the biggest problems with interstellar space flight is that communication and power supply can become a problem. Some years ago I had an idea which I called "Energy Link", which would be able to solve the problem. The solution is very simple: The interstellar space craft has a manufacturing facility on board to manufacture satellites that are used to link back to Earth. During flight, in strategic locations, a satellite is dropped that communicates with satellites dropped earlier. Energy is transmitted by using microwaves, for instance. This way, not only communication could be maintained over vast distances, but also power supply in mid-space when there's no sun around. The satellites would be powered by the energy transmitted to them, or by internal power plants. Supporting vehicles transporting freight could travel to the remote craft and between satellites. If enough support vehicles exist, then a bucket-chain like system can be used, so that there's always one vehicle arriving when another is leaving. Such a system could also be used to establish or maintain space infrastructures.
With interest I read the Wikipedia article about space elevators, and I remembered an old idea of mine that I had during a discussion with a co-worker about 11 years ago. Of course, it might sound like a stupid idea at first, but why not build a space elevator that just reaches out of Earth's atmosphere? That is built like a tower, about 20 km across and of similar height (or more, depending on how little density of atmosphere is desired). A sufficiently thin wall could house all sorts of space-port businesses, while a center platform, almost 20 km across, would be used to lift spacecraft to and from the high end of the tower. If the tower just reaches out of the atmosphere, spacecraft would still have to overcome gravity, but they could do so (almost) outside the Earths atmosphere. A honeycomb lattice like structure could provide enough structural integrity, and leight-weight materials could keep the overall mass low. This could also be used as a construction site for more refined space elevators that are attached further up in space.