For those of you having RSI issues with mouse, here's a highly recommended mouse:
Evoluent VerticalMouse for left hand
The Evoluent VerticalMouse is favored by the well-known programer Jamie Zawinski (aka jwz). See Celebrity Programers with RSI (Repetitive Strain Injury).
A similar one is Microsoft's ergonomic mouse, the Natural 6000.
Or, you can try a trackball: Best Trackball Mouse, or touchpad Best Input Devices (Jog/Shuttle, Touchpad, Cyborg Mouse, Pen Tablet).