Don't you feel that PCs should have more knobs? Ever since I saw some really nice demos of Soft|Image a few years ago at ECTS, I have been hankering after some. They had a Peavey MIDI contoller box, with 16 sliders, and a bunch of buttons and dials hooked up to various animatable parameters within SI to allow them to use the model like a puppet, in real time. Very neat.
3D Studio Max also has MIDI input as a potential controller for any parameter (colour, size, position, rotation, fade between two textures...).
Build your own PIC-based MIDI controller explains the basics, and has plenty of links to other pages with more info. Of course, a USB-based box o' knobs might be nicer, but MIDI is already supported by most OSes. I daresay you can write a MIDI plugin for Girder to get contol of most of Windows from the knobs without dealing with all the automation side from scratch.