Doesn't look too safe, but pretty cool...

motorcycle

...This year's show, however, had one very unusual one-off custom, the Uno. The orange and grey coloured Uno made its first public appearance balanced on its two side-by-side wheels and its footpegs. Looking more like it should have been ridden by George Jetson as he pulled up to his space platform, it looked out of place amid the other custom creations in the building. Perhaps that's why it garnered so much attention. 

http://blog.makezine.com/archive/2008/04/the_uno_a_one_wheeled_mot.html?CMP=OTC-0D6B48984890 

I hope they worked out that problem where the thing suddenly goes into reverse and ejects the rider.

The voluntary recall of all Segways in September 2006 is related to a software glitch. The malfunction causes the wheels on the device to suddenly start moving backward when a number of factors align. The details right now are a bit spotty, but it appears that the problematic circumstances begin with the Segway's "speed limiter."

 http://travel.howstuffworks.com/segway-recall.htm