Sideway uses lean angle to control speed, and a wireless Nunchuk controller to steer. There are two 280W, 24V electric scooter motors, one on each wheel, driven by a Sabertooth 2x32A motor controller. The batteries are 3 cell, 5 Ah lithium polymer, normally used for model aircraft. It'll go about 40 minutes or so on a charge, depending on what you're doing.
I'm running a Parallax Propeller with custom software for the IMU and control.
It gets a good amount of attention. :)
I have the next version planned, and all the parts are here, I just need the time to work on it. It'll have a wider wheelbase, belt drive instead of chains, and a shorter board. I may also use a proper skateboard or longboard deck and put some grip tape on it.
Hanging out at the local craft store:
It'll go about 10 miles per hour (this clip is probably close to that):