Trackman Marble
Used by 2 peoplelogitech.com ↗

“I use Apple laptops that are light enough for me to carry around easily, the same Logitech trackball I've had for 15 years, and a big bright high-res monitor because of eyestrain.”
Erin Kissane Interview, Writer, editor (Source) · via Uses This 
“I prefer trackballs over mice and use a Logitech TrackMan.”
Eric S Raymond Interview, OSS developer, writer ('The Cathedral and the Bazaar') · via Uses This