Smule has released the Magic Piano application exclusively for the iPad. The application was inspired from renowned pianist Lang Lang. Smule is also best known for developing the iPhone apps I Am T-Pain and Ocarina.
You can customize how many keys you want on the Magic Piano. The app also lets you play the piano in circle form. The piano has preloaded songs that show the keys lighting up as it plays so you can learn how to play certain songs [iTunes link].
Check out the video demo below of the app: