It also depends on if you are going to use your Arduino to drive Servo's. Many people get confused on the issue, you can use the Servo Library and drive any servo with a Digital pin.
I'm not for sure what your purpose is for the PWM, but if it is Servo's, see:
Arduino Playground - HomePage
If you are looking for continuous rotation ideas (robots, etc):
Continuous rotation servos and Arduino - Bajdi electronics
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