CadSoft Eagle

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.

Learning

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

Instructables

• Draw Electronic Schematics with CadSoft EAGLE
• Turn your EAGLE schematic into a PCB
• Make hobbyist PCBs with professional CAD tools by modifying "Design Rules"

Parts Libraries

• Sparkfun Eagle Library
• CadSoft's user-contributed libraries