Used to use an old Logitech Trackman Marble+, but they only came with PS/2 connections and XP drivers. As such, I had to give it up when I got my new computer, and since there aren't any other trackballs that size out there(my hands are big) I've missed it. Closest thing I could get was their new M570 wireless trackball.
stray, I fixed your url. No need to include quotes or put in the http://, it just tends to break the tag.