Jerome Demers who is currently an intern at Solarbotics created this Miniball Solar Robot.  Since it doesn’t just drive around it seems to have a mind of its own.

"This robot uses a solar engine circuit. A small solar cell by itself generally doesn’t have the power to make a motor move, so you have to store this power up in a capacitor, which is a small battery-like storage device. When the circuit sees that there is enough power stored, it releases it in a burst to the motor, getting useful work."