gTar has been making the rounds lately, being covered on many of the major tech blogs such as TechCrunch and Engadget. It's a kickstarter project that enables anyone to play the guitar.
To get started you just dock your iPhone (shame it's already limited to an iPhone), load up the gTar app, pick a song and then you can follow the song on your iPhone while little LED's light up along the fretboard that will show you how to play. It's literally as simple as that, you just go through the three levels available whilst you get better and better.
The project's goal was to acquire $100,000 in funding but it's already beaten that and doubled it. It's still got just under a month before the project stops receiving money so who knows how much it will amount.