The Kensington Expert Mouse (http://us.kensington.com/html/2200.html) is a simple, elegantly designed trackball which has been popular in the assistive technology field. It has four buttons which can be programmed to perform various mouse and navigation functions. Typically, I open up the casing to switch adapt the buttons, so that any type of switch can be used to activate the buttons. This is especially important for a person who may have limited hand movement, or may be using his/her chin to use the trackball.
One gripe I have is with the wireless version of this device. The speed of the cursor movement is hard to control. Sometimes changing settings within the Kensington Control Panel has no effect at all on this function. In general, the Kensington software can be unpredictable at times.
