Someone on FurryMUCK posted some photos of their Beta Pen and it looked interesting enough that I ordered one for myself.
The Beta Pen is actually fairly old technology. In medieval times, scribes would write using a silver-pointed stylus. The Beta Pen's point is a metal alloy, there's no graphite, no ink. It writes like a pencil and leaves a pencil-like mark, but it's extremely difficult to erase and the point wears extremely slowly. It can write underwater, in freezing cold or upside-down. It won't leak, dry out or smudge and only rarely requires sharpening.
There are three versions, one the length of a standard pencil, a pocket version about 3.15 inches long with a cap, and a very short 2.15 inch version that attaches to a keyring.
The only real downsides are the rather high price tag, about $24 each, the tip is sensitive to impact and the pencil-sized version doesn't come with a cap.
It probably wouldn't be very useful for art, as it cannot be easily erased, at least not without damaging the paper. The smaller capped versions would be great for an emergency kit or to keep in the car. Because it does not smudge, it would also be particularly useful for southpaws.