How can I mirror my iPad display wirelessly? I am looking to display my iPad screen wirelessly to an external display to demo applications.  I found this video showing exactly what I want to do with an iPhone but no explanation as to what the hardware dongle used was.

The main thing is that there isn't a wire tethering the user to the external display.
This is possible using iOS 5 and an Apple TV using AirPlay.

This only works with iPhone 4S and iPad 2 and all video and sound are mirrored wirelessly to any TV that is connected via HDMI downstream from the Apple TV. You do need a wireless network for the two devices to communicate. 


  Just double-click the Home button, swipe all the way to the right, and
  select AirPlay Mirroring.


Reference: http://www.apple.com/iphone/features/airplay.html