IMO the king of the trackballs, Microsoft Trackball Explorer. I thought I had lost the ball but just found it - you can see the amount of use from how the paint
IMAGE Trackball Mouse Wireless USB Hanheld Wireless Mouse with Control Pointer for Right or Left Hander Users
Logitech MX ERGO Wireless Trackball Mouse with USB Receiver│440 DPI│8 Buttons | eBay
Kensington Orbit TrackBall - Wired Ergonomic TrackBall Mouse for PC, Mac and Windows with Ambidextrous Design, Optical Tracking & 40 mm Ball – Space Grey (64327EU), Silver : Amazon.co.uk: Computers & Accessories