I ordered a M570 to try out. Will try to post a review sometime.
Show Image
(http://lh3.googleusercontent.com/public/rEEDTqNcs9M_MLE4K0QLvtc9BhHoeDuZhO6CA3LC4GLPraMW8BuMjMPPIhzLi_7wQWd4XFsfnHpefx_IO5uQLz8pmmhXtUdrwVu-lcBnNtLoY-2OZspxNGM4PDEM)
Good.
Here's a weird one from Fentek. Could probably cut off the wrist rest part. A Serial Port Logitech is on Ebay. The advantage of this is USB (although through a dongle).
Link (http://www.fentek-ind.com/mwrtbb.htm).
Show Image
(http://www.fentek-ind.com/mwrtbb.jpg)
Yes but probably is still not optical, so modding it would be pointless.
A couple of that trackball are present on ebay
Dell (http://cgi.ebay.com/Compaq-Trackball-Ballpoint-Mouse-Vintage-Clips-2-Side-/320678704406?pt=Mice&hash=item4aa9f0b516)
(http://i66.photobucket.com/albums/h277/rouge-1968/1%2020%2011%20uploads%20for%20afternoon%20list/175.jpg)
and logitech (http://cgi.ebay.com/Logitech-Trackman-Portable-mouse-trackball-new-Serial-/230603079979?pt=Mice&hash=item35b103c12b)
(http://i.ebayimg.com/00/$(KGrHqJ,!gwE160cou),BNkrC1pRU!~~_12.JPG)
The dell one is very cheap if anyone wants to try it.