SpikeNav is a system for 3D navigation that exploits standard stylus hardware---in particular, the extra tilt and pressure input channels that it provides over a standard mouse.
An extended abstract describing it: bridson-uist09-spikenav.pdf. The accompanying poster: spikenav_poster.pdf.
Here is example code, released into the public domain:
And, also, here's the UIST Madness video that unfortunately didn't play properly at UIST: spikenav_madness.mov.