On this page, we'll tell you about ordering components for any of the listed OpenMaze shields and projects, and the vendors we like for general components. I've found that hobbyist sites are a good place to start, and then go to Digikey or other professional vendor when you know exactly what you need.
Sparkfun is a great website both for many reasons, and was my first entry into open-source hardware. Aside from offering a large selection of different basic components, Arduino/Raspberry Pi's, and break-out boards (easily connectable boards carrying integrated circuits, e.g. accelerometers), they have numerous educational resources for learning programming and electronics.
Digikey is the standard electonics component supplier, with literally millions of different products. It's kind of hard to find things if you don't know exactly what you need though, so you might want to go to one of the hobbyist suppliers that carry the most frequently used components when you're starting out.
AllElectronics is a surplus electronics supplier that has almost the cheapest prices on basic electronics components, motors, connectors, etc. IF they have what you're looking for! I always check them first for buying cheap components, especially when prototyping.
Adafruit is similar to Sparkfun but has a number of additional boards and kits of its own design. It can also be a good vendor for SoC/RaspberryPi components such as small LCD screens and other components for embedded projects.
Modern Device is where we get out bulk headers (which we frequently use in our OpenMaze shields) and our analog Hall effect sensors. They also have lots of other components, overlapping with Sparkfun.
Abra is another super-cheap electronics supplier, like AllElectronics, but with a larger selection of multiple-conductor wires and connectors, like D-SUB and IDC/parallel/ribbon cable connectors.