The TLC5940 is a powerful chip for pulse width modulating . You can control 16 channels with 12-bits of resolution, which means you can write out analog integer values between 0 and 4096. The TLC5940 is a bit like an analog version of a shift register . Sparkfun has a breakout board , or you can get the raw chip in a few different packages at digi-key, or mouser. The TLC5940 is made by Texas Instruments . They describe it as an LED controller, but since it outputs PWM on all 16 channels you can also use the TLC5940 to control servo motors. Nice tutorial on Servo motor control with the TLC5940 at bildr.