This 3D printed polyhedron by Leonardo da Vinci is a great example of what a 3D printer can do. At first, I printed a small version of it, about 2 inches in diameter. My son liked it and asked me to print a larger one in red for him. At the larger size, the print required full support, and it took about 18 hours to print. This was printed in ABS @ 0.2mm layer height.
The model can be found here: http://www.thingiverse.com/thing:156482 (model credit: Roger Peng)