So my goal for this project is to have everything 100% off the shelf so anyone can built this.  There will be zero (yup, zero) custom parts.  Everything can be bought with zero alterations (I hope).

So my first parts ordered are actually the inner ear of the board.  I ordered all three parts from Sparkfun.

1 x IMU 6 Degrees of Freedom - v2 with ADXRS150 (SKU#: SEN-08192) = $324.95
1 x Battery Holder - 4xAA Square Terminated (SKU#: PRT-08159) = $3.95
1 x RS232 Shifter SMD (SKU#: PRT-00449) = $13.95

The Inertia Measurement System (IMU) is what will allow me to know exactly where the hell I am.  I'm not sure if this will actually eliminate the need for force sensors to detect someone turning if this is sensitive enough.  I need the shifter to communicate with a computer and the batteries to power the IMU.  Now that I have these, I can start building out my test applications for detecting movement and even creating the inverse pendulum app maybe out of some LEGO.  Trevor Blackwell has tons of information on the topic of home built segways too.

And my ultimate goal is to have a cell phone power (looking at a spare iPaq hw6925 that I have) this bad boy but no promises, I may have to find a lower powered embeddable computer for this.

Next items that need to be bought are the motors, gearbox and motor controllers.  I have a few options on this front but I think I found my wheels and gearbox.