Laptop Trackball

[JimS]

I'm still in love with my IBM T40.  It has both a touchpad, which I use, and a pointer stick, which I seldom use.  However, I don't love either of these devices.  I don't know why trackballs are used on laptop/notebook computers; they used to be on some models, and I think they're much easier to use than touchpads and pointers.  I seem to recall a few years back a small trackball that could be clipped onto a laptop/notebook, but I haven't been able to locate one.  Are these still made?  Does anyone have any leads on them?

Thanks.