You may have heard of Reprap, the 3D printer that prints itself, but if not, I'm sure it'll make you curious. The idea of 3D printers is that you can "print" 3D objects you've designed on a CAD program. Reprap printer or MakerBot are machines that can create 3D plastic objects by fusing plastic into small plastic spaghetti (that adheres itself while hot) over a movable table. Objects are created putting one layer on top of the other.
Given the fact that you can print 3D plastic objects, Reprap project went on to do design in such a way that a finished Reprap printer would be able to print all the plastic pieces to make a new one. Unfortunately metal parts and electronics still need to be bought elsewhere.
Care has been taken to provide open specification for all the components so anyone can build their own easily. Reprap first version was named Darwin (shown in the picture) but a new version is out, named Mendel, with many improvements, smaller footprint and better performance. The project however is a bit weak on detailing how to make your own Mendel if you do not have a friend to print you the parts.
Update: Well, maybe details on how to build Mendel are not so sketchy, but I failed to find them.