I've been very pleased with my Microsoft Trackball Explorer 1.0. It's USB, has four programmable buttons (apart from click and right-click, I use the other two for forward and back in browsers), a clickable scroll-wheel (normal scroll traverses content line by line, click + scroll pages up and down) + the trackball itself which I can't imagine doing without. I used to have a wireless mouse but couldn't stand the whole recharging/battery changing hassle. All the best, Colin.