The Kensington "expert" trackball. Here Big and sturdy, stays in one place so you can whack the scroll ring or paste button without looking. Most of the time my hands are on the keyboard, and when they're not I don't want to go mouse hunting. Not cheap, but TANSTAAFL.

Oh sure... http://upload.wikimedia.org/wikipedia/en/d/da/HA_WhippedCream.jpg