The Leonardo is the newest in the Arduino family. Using the ATmega32U4 as its sole microcontroller allows it to be cheaper and simpler. Code libraries allows the board to emulate a computer keyboard, mouse, and more.
The Leonardo even sports 12 analog inputs! And since the communication with the computer is done through a simulated serial port over USB, the hardware serial port on the processor is free for your applications.
Note: This board has just recently been announced so we do not yet have a full datasheet or list of specifications. Backordering allows you to be one of the first on the block to get the new board. We expect our first shipment within the coming weeks, but due to the popularity, it may not fill all existing backorders.