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
Logitech MX ERGO Wireless Trackball Mouse with USB Receiver│440 DPI│8 Buttons | eBay
Logitech MX Ergo Wireless Trackball Mouse
L-Trac Blue Trackball
IMAGE Trackball Mouse Wireless USB Hanheld Wireless Mouse with Control Pointer for Right or Left Hander Users