Synthesia - A fun way to learn how to play the piano.
Cheeky Fingers - Piano Chord Dictionary, Progressions and Suggestions
Piano From Above - Piano From Above is a program that turns learning the piano into a videogame.
Playground Sessions - Online piano learning game.
Simply Piano - Fast and fun way to learn piano
Linthesia - Linthesia is a game. A game of playing music! You only need a MIDI file