While visiting Tokyo, I spent some time in Akihabara where I stopped at the vStone Robot Store. I spotted a new balancing bot they had called the Beauto Balancer Duo (Reseller with English translation) and brought one home. Two motors mount under the circuit board and use encoders. The two AA batteries are mounted high up with spacers to raise the center of mass. An optional radio control module (shown in the photo) mounts to the front and pairs with the controller shown in the second photo. There's also an optional line follower which can mount to the bot.
The video below shows the bot balancing while being driven around remotely. To start it balancing one connects the battery and hits the initialization button while holding the robot in balance -- and then lets go after a couple seconds. I haven't analyzed the bot in any detail yet. One can download software for tweaking the controller parameters. Unfortunately I was only able to download the Japanese version and I didn't get a response from vStone on the availability of an English version (although it appears one of the resellers has an English version).
The vStone store is located near Akihabara in the center of the inset map below. The area is a hotbed of hobby robotics. We also stumbled across a humanoid robot competition just after leaving the store.