Long-term use of a mouse is far more likely the cause of repetitive stress disorders such as Carpal Tunnel Syndrome than the much maligned keyboard! An ergonomic mouse or tracking device that is properly sized, properly located, properly adjusted AND which is selected based on the requirements of your job is a vital part of your workstation.
There are a myriad of mice and other tracking devices on the market, but only a few that we feel are worthy of being called "ergonomic". A good ergonomic mouse provides a neutral wrist position, size and sensitivity adjustments.
Pictured at left: Humanscale Switch Mouse