Technology makes a very nice, if pricy, controller
knob called the Powermate
that plugs into a USB port.
It's a beautifully machined, free-standing aluminum knob,
with a glowing blue base (looks sharp, and makes it easy to find in the dark.)
I've been looking for a good-feeling, cheap rotary controller
for a long time, and while this isn't it (at $45, I can't
justify a dozen of them), at least it's got the good-feeling