If your looking for a more physical way of interacting with your touchscreen DSLabs have come up with a neat hack to allow you to use physical knobs to act as rotary inputs. Check out a video of the knob hack in action after the jump.
Acting like a soft stylus the device uses and conductive path from your hand to the screen. DSLabs started using copper tape, conductive fabrics and wires with two touch plates on either side of the knob. With careful positioning the screen then reads the movements of the physical knob and translates them into movement.
Via Oh Gizmo Via DSLabs