The Roly-Poly Pot tips over when the plant needs water. The agua inside is off center and balances a counterweight in the base. The design, by Samgmin Bae, is meant to indicate when the plant is thirsty, but with the automatic movement, it shouldn't be too hard to rig up a self watering version.
The best part, though, is the introduction to this concept at Yanko Design:
Product page [Yanko Design via Make]
