Arduino 20 Servos, 4 Pins, Variable Refresh Rate
Some time ago I posted a library for running ten servos from an Arduino using just 2 pins. I have extended it to 20 Servos from 4 pins.
The library has a variable refresh rate determined by the number of servos, servos can be split across two banks for higher refresh rates.
Original 10 Servo library with all the background here -
New version with support for split banks for higher refresh or just more servos here -