First featured on the iPhone, Pianist Pro puts the power of professional grade pianos at your fingertips. It comes with 16 professionally recorded instruments: pianos, synths, guitars, and organs. Just because it's on the iPad doesn't mean you can't get the full key experience, either-you can configure the onscreen keyboard to display the full 88 keys. While you're on the go you can use a MIDI keyboard instead of the onscreen offering, record your work, then export it via WAV files when you're back in the studio. This is the best piano app you can buy and it's only $5.