Haven't you ever wanted an Etch A Sketch right there, on your DS? (We hadn't considered the possibility until today.) For $25, and some familiarity with homebrew apps, you can get a DS motion card, which includes a 3-axis accelerometer and a single-axis gyroscope. Apparently some folks have already cooked up some apps that will work with this card, including an Etch A Sketch-style application and two games. You can plunk down the cash for the pre-order, but if you want something a little more immediate, you could just buy a regular Etch A Sketch for far less, and not have to worry about all that homebrew stuff. Your call, though.
[Via DS Fanboy]