This is a must for robotics!

The Adafruit 16-Channel 12-bit PWM/Servo HAT will drive up to 16 servos or PWM outputs over I2C with only 2 pins. The on-board PWM controller will drive all 16 channels simultaneously with no additional Raspberry Pi processing overhead. What's more, you can stack up to 62 of them to control up to 992 servos - all with the same 2 pins!

All that for $17.50.

Works with any servo that can be powered by 5V and take 3.3V logic level signals.

More information.