NXT Shield Library
After several questions on how to use the NXT Shield I decided to create an Arduino library. All the code is available at github: https://github.com/TKJElectronics/NXTShield.
The library is pretty easy to use, I have provided three examples witch demonstrates all the libraries functionalities.
I works with all official Arduinos including Arduino Mega. To use the ultrasonic sensor with an Arduino Mega, one have to connect pin 20 (SDA) to A4 and pin 21 (SCL) to A5. A new revision of the shield might use the two extra SDA and SCL pins that are near to the AREF pin on r3 versions of the new Arduino boards.
Below are some photos of the NXT Shield: