Or a clone of SparkFun's ProMicro, which is absolutely awesome. It's basically Arduino Leonardo (Mega32U4) in the 'micro' form factor and able to work either on

Or a clone of SparkFun's ProMicro, which is absolutely awesome. It's basically Arduino Leonardo (Mega32U4) in the 'micro' form factor and able to work either on 3.3V or 5V. You can get it at around $3