Standard servo - TowerPro SG-5010 - 5010
This high-torque standard servo can rotate approximately 180 degrees (90 in each direction). You can use any servo code, hardware or library to control these servos. Good for beginners who want to make stuff move without building a motor controller with feedback & gear box. Comes with 3 horns, as shown. They aren't the highest quality servo (which is why they are less expensive) and so are not suggested for hobby planes.
To control with an Arduino, we suggest connecting the orange control wire to pin 9 or 10 and using the Servo library included with the Arduino IDE (see here for an example sketch). Position "0" (1.5ms pulse) is middle, "90" (~2ms pulse) is all the way to the right, "-90" (~1ms pulse) is all the way to the left.