Bay Area Hobby Supplies
Hobby Engineering
Berkeley Ace Hardware
Electronic Kits
Goldmine Electronics Electronix Express
Jameco Elenco Quality Kits
Electronics123 Solarbotics
Electronics
Digikey Mouser
Mechanical
McMaster-Carr Small Parts
Materials
Tap Plastics Online Metals
Springs
Century Springs
Controllers
Sparkfun
Instructional
All About Circuits (really useful)
Make Magazine Instructables
Discover Circuits Schematics
Adafruit Sparkfun
Robot Components
Pololu
Arduino stuff at NKC Electronics
The Original Arduino Website