MAKE Flickr Pool member Funax made an Arduino-compatible board powered by a single AAA battery. A step-up converter is used to boost the battery’s 1.5V output to 5V and meet Arduino’s minimum power requirements. Keep in mind – this circuit would considerably reduce current supplied to the board and therefore limit its ability to power external components.
Related: Uduino – Low cost Arduino development boardLink
Arduino @ MAKE – Link