One of the main problems with making your own circuits is the tricky and often dangerous soldering process, so Instructables user Mikey77 has come up with a solderless 3D printed circuit.

It is the same size as standard 1/16" thick, through-hole soldered perfboard, and can be made a little quicker than soldered circuits, but it does require a bit of skill to make.

This example is a simple micro-controller circuit that flashes three LED's in sequence.

It was made on a MakerBot Replicator 2 with PLA filament and is intended to be a minimal illustration of what is possible.

In order to avoid using a soldering iron, he uses a commercial conductive paint, though he does include recipes for making your own conductive glue here and here, as well as recipes for conductive rubber here and here.

If you don't want to make the circuit yourself, you can also send the stl file to Shapeways, or another commercial 3D printer.