Raspberry Pi Ladder Board
Possibly my first real soldering project, unless you count the much simpler GPIO expander kits I put together. The Raspberry Pi Ladder Board is a great into to soldering and an even better intro to Raspberry Pi GPIO. It also looks pretty! It's not quite a rainbow, but it's close enough.
The 10 LEDs and 4 buttons are plenty to get started with and are handy for testing basic GPIO access from scripts.
I've taken the time now to liberally photograph my board but still haven't yet put together any Ruby examples for it. They're in my todo list, but I'm spending some time brushing up my Ruby skills so I don't end up creating bad examples.