This Led Matrix Dice made by Itay Donenhirsch looks very cool. Give it a shake to roll a new number.

"The cube is driven by three 1.5V small button cells (which are sold here as batteries for EasyPark computerized parking ticket). The brain of this gadget is a ATmega168. The ATmega168 is programmed using avr-gcc and avr-libc. The MCU is connected to the matrices using a ULN2008 as a current sink and a 74LS164 as led driver. For extra fun I pulled a speaker from a Nokia mobile phone and connected it as well."