I’m not sure if these have been previously posted, but how about…
Accelerometer-Lets your robot know which way is up and when your robot tilts left or right, up or down, or side to side.
Compass Sensor-Tells your robot which direction it is facing.
Gyroscopic sensor-Allows your robot the ability to detect rotation.
These are from sensors developed by Lego for the Mindstorms NXT series, and i think they would be pretty cool to have on our VEX robots.
Here are the Lego versions from their site…
http://shop.lego.com/ByTheme/Product.aspx?p=MS1040&cn=17
http://shop.lego.com/ByTheme/Product.aspx?p=MS1034&cn=17
http://shop.lego.com/ByTheme/Product.aspx?p=MS1044&cn=17