The tiny $US35 Raspberry Pi can do all sorts of amazing things, but nothing is labelled that well, and connecting it to a breadboard isn't always obvious. DIY enthusiast Monk created a printable sheet -- dubbed the Raspberry Leaf -- to place over the Pi.
The Raspberry Leaf sits directly on top of the GPIO so you can instantly see what each pin does without referencing a manual. It's a big help when you're trying to piece together your electronics project. The Raspberry Leaf is free, and all you need is a printer. Head over to Doctor Monk's site for the PDF version.