We've seen Segways built partly from Lego before, but a Segway built entirely from the Lego in a standard NXT 2.0 set? That's something special.
What's particularly cool about the NXT Segway is how it balances itself: instead of using a gyro sensor, it leans on the NXT colour Sensor in light sensor mode to detect its angle relative to the ground. It's controllable via Bluetooth, and has that certain Wall-E-esque feel that makes me feel all fuzzy inside. Complete instructions to make your own are riiiiiggghhhht here. [NXT Programs via The NXT Step via Make]