Lego robot is a cheaper alternative to a (too) expensive LEGO NXT. Two HUB-ee wheels are used for driving. It is controlled by two AVR microcontrollers - ATTiny 2313A takes care of PID control, soft-power button and USB communication over ft232, ATMega 32A is user programmable (over USB and ATTiny) and it controls everything else. On main PCB are also a 1117 5v regulator, standard hd44780 2x16 character LCD, a few buttons, a speaker and connectors for external sensors and LEDs. LM393 double comparator is used for low-battery indication and MCU cut-off. Also included are Gens eco 1300mAh 2S 7.4V Li-Po battery and a charger.
Check out my Lego ball contraption movie to see it in action.