The RedBoard is quite possibly our favorite Arduino-compatible microcontroller. The folks at SparkFun took their years of experience with microcontrollers and made their own. The RedBoard can be programmed over a USB Mini-B cable using the Arduino IDE. Select "Arduino UNO" as the board type and you are ready to go.
The RedBoard has 14 digital I/O pins, 6 PWM pins and 6 analog pins. This is perfect for many of the projects you'd need a microcontroller of this size. It also has the standard Arduino UNO R3 footprint so most shields are compatible. You also can power the RedBoard over USB or through the barrel jack. The on-board power regulator can handle anything from 7 to 15VDC.