The internets provide a million places to purchase electronic components for the part-time hobbyist like myself, but lots of them seem to cater to the wealthy full-time hobbyist. I'm keeping a list here for my own reference.
- futurlec: "The electronic components superstore". Has surplus and new, including lots of cheap stepper motors, interface boards, and other random stuff.
- MPJA: Lots of assorted used/new stuff, for quite cheap, including lots of power supplies, like this one.
- Ebay: If you're willing to wait, you can get pretty much anything cheap from China.
- Continuum Technologies: Canada-based vendor of all sorts of interesting things, including some cheap, small, LCD displays.
- iStore (iteadstudio): Arduino stuff, shields, (cheapish) displays, kits.
- Electronics Goldmine: Surplus stuff, tends to be cheapish.
- All Electronics: Surplus stuff, cheap.
- Alltronics: Cheap surplus.
- Seeedstudio: Arduino/robotics stuff, tends to be more expensive, like sparkfun.