Falcon Friction Thumb Shifters
These thumb shifters are unusual because they fit on both road and MTB sized bars. Therefore, they fit on all handlebars. They even work on drop bars, but not on the sleeve.
They are not Campagnolo quality (what do you expect for $16 per pair) but they do function perfectly, and the soft rubber tipped levers are actually very comfortable. Cables are included. Price is per pair, a left and a right.
Satisfying ratchet action. Classy vintage Japanese camera spec plastic covering.
I bought these because the grip shifter (Shimano Revo-Shift) on my folding bike wore out and didn't work any more. I didn't want to replace it with the same unit, because the grip shifter was full of small plastic parts, was overly complex and obviously prone to breakage and wear.
A thumb shifter seemed to be the obvious way to go. The Falcon unit was cheap, simple and easy to install. And it shifts as well as the indexed grip shifter. It actually shifts a bit better, in fact -- shifts are smoother and quieter.
The Falcon shifter comes with cable and cable housing. One little nit is that it does not come with the nut needed to secure the shifter to the handlebar (5mm, if I remember right). Also, it comes as a pair -- left and right, front and rear derailleurs. I only need the rear, but it's inexpensive enough that it doesn't matter.