Ask non-artists to draw a picture, and most will say "Oh, I can't even draw a straight line." Nobody can draw a straight line without using a ruler or something. The arm doesn't move that way. The nature of the shoulder, elbow and wrist joints support moving a pencil in nice curves and arcs, but not really in straight lines.
The same is true for scroll bars and sliders in graphical user interfaces. Yet these things are everywhere, requiring the unnatural straight line movement to scroll up or down a page, left or right, or to set levels on things that can have their levels set. In the old days of computer graphics, you could get a box with a bunch of knobs on it, and have your program use those knobs to set whatever levels need setting. Unfortunately, that's all but disappeared.
Now, I'm not planning to plug products in this space, so I'll only write about things I know nothing about (which goes for most of the content here.) However, at first blush, the Logitech NuLOOQ seems very promising. I got a chance to play with this at SIGGRAPH this past summer. It's got various places where you can twist, spin, and press to get the effect of knobs and shuttle wheels. You can use it with Photoshop, to scroll around the art, change brush sizes, etc., all with your left hand, while your right hand is wielding the stylus from your Wacom tablet. Together, these gadgets make drawing pictures on the computer almost like ... well, like drawing pictures.
Are you listening, Santa?