References:

nBot :  Developed by David Anderson of Southern Methodist University.  This site contains all sorts of interesting links regarding balancing type robots.  Lots of video of nBot negotiating various terrain.

Homebuilt Scooter : Trevor Blackwell, a California inventor built his own balancing scooter for about $1500.  He gives a breakdown of the parts he used.  Site includes some video of his operational scooter.

Segway Human Transporter :  Dean Kamen's revolutionary invention that is 'supposed' to alter the way we view urban transportation.

iBot Mobility System:  Another Dean Kamen invention, now underwritten and marketed by Johnson and Johnson.  A stair-climbing and balancing wheel chair.

JOE:  A French radio-controlled balancing robot.  A lot of good videos of JOE negotiating various terrain.

AutoBender:  A series of robots designs and incarnations.

Loony-Cycle: The Bolton Technical School near Manchester England built this remote-controlled single-wheel robot as a design project.  It uses small fans and tire geometry for steering.