You can make a lot of cool DIY electronics with an Arduino board, but you can actually make your own Arduino for a fraction of the cost -- with a bit of room for customizability, too.
Obviously, it's easier to just buy an Arduino, but if you feel like doing a bit of extra tinkering -- and saving a few bucks -- Instructables user Higgs Boson has you covered with a step-by-step tutorial for creating your own Arduino. It's about half the price of the Arduino Uno ($US15 compared to $US30), and you have room to do away with any stuff you don't need on the board for space savings.
Check out the link below for the full how-to, and be sure to check out all of our favourite Arduino hacks if you're short on inspiration.
How to Make Your Own Arduino Board [Instructables]