I gave a presentation to the Oh-Ky-In Amateur Radio Society on August 6, 2013. This was an update of the presentation I gave to the Cincinnati FM Club in February, which was an update of the presentation I gave to the Milford Amateur Radio Club a while back. This page is a set of links for those that attended or missed the presentation.
Presentation: Introduction_to_Arduino_Microcontrollers (PDF warning)
Have an Arduino board but not enough accessories or don't know where to get started? Seeed Studio has a "Sidekick Basic Kit" that can get you up and running - it doesn't have an Arduino, but it has a lot of components (etc) to get you started. And it's $20. Seeed Sidekick Basic Kit ($20)
NOTE: Look hard at what these packs include! There ARE differences.
Raspberry Pis and Beagleboard Blacks can be bought at Mouser, Digikey, and Newark Electronics/Element 14. Raspberry Pi accessories (like the Pi Plate an Pi Cobbler) can be bought at Adafruit or Newark Electronics/Element 14.