CadSoft makes EAGLE, a popular piece of software for designing electrical circuits and laying out PCBs. It runs on Windows, Mac OS X, and Linux. There's a free (as in beer) version available for non-profit use.
 Sparkfun Tutorial Series
- Getting started with eagle
- The basics of laying out a PCB with eagle
- How to create a custom footprint & part in eagle
- Draw Electronic Schematics with CadSoft EAGLE
- Turn your EAGLE schematic into a PCB
- Make hobbyist PCBs with professional CAD tools by modifying "Design Rules"
- How to make a custom library part in Eagle CAD tool
 Parts Libraries
 User Language Programs (ULPs)
- epscdraw_411.ulp outputs color EPS (encapsulated PostScript). Handy for printing