This is the brains of your Speeduino. Every shield type Speeduino needs one, including the 0.3.x, 0.4.x, NO2C, and UA4C. Every MEGA I sell now has the DC power jack removed. The jack is not used in the Speeduino environment, and it gets in the way a little on the NO2C and a lot on the UA4C. Aftermarket, brand varies.
Use SpeedyLoader to load your Arduino MEGA with Speeduino goodness.