The L-Trac trackballs have a large free spinning roller above the buttons (which surround the trackball itself). I find it really nice for navigating text in on

The L-Trac trackballs have a large free spinning roller above the buttons (which surround the trackball itself). I find it really nice for navigating text in one dimension. When I was really working on the ergonomics of my setup I experimented a bit with a space mouse in my opposite hand to act as a 2d scroll device, which I liked pretty well, but I don't bother with it.