Fritzing is essentially Electronic Design Automation software suited to the needs of designers and artists. It uses the metaphor of the breadboard, so that it is easy to transfer a hardware sketch to the software by using a drag-and-drop-based GUI to copy your sketch. From there it is possible to create PCB layouts for turning your prototype into a robust PCB, either on your own, or with the help of a manufacturer.
WWW: http://fritzing.org/