Self-balancing unicycle

The SBUV3 is a self-balancing, motorized electric unicyle that you steer by shifting your center of gravity. They cost about $1800, feature regenerative braking, and have a top speed of 12.5mph. The steering software adapts to you (and vice-versa), fine-tuning its responsiveness based on your riding-style.

One Wheel. ∞ Fun

(Thanks, Rob!)