I've been using a Kensington Orbit (with scroll ring) trackball along my EZ, and it's lovely. With a trackball, you don't necessarily need to mod your keyboard, yet, your hand moves a LOT less than with a mouse. The Orbit so far is superb, the ball is easy to control, took about 15 minutes to get used to it (though, precision is a bit of an issue, but I at least don't need all that much of it). And the scroll ring is orders of macnitudes better than any scroll wheel I have tried before.