iAno really uses the multi-touch functionality of the iPhone by allowing you to basically play piano on your iPhone. This would really be a great app to show off what your iPhone can do and it will surely give the iPhone some wow factor. The application was developed by someone going by the name Mr Aardvark and gives you a 4 octave keyboard with arrow keys at the top of the screen to navigate around the piano.
Mr Aardvark is planning on updating the app to use a full 88-key keyboard, switchable sample sets, recording and playback, as well as support for loading .MID tracks.