Apple showed everyone how GarageBand for iPad can teach non-players how to strum like a pro, but if you’ve already got a guitar (and the skills), this $US99 Apogee JAM studio-quality input can connect the two together.
Frustratingly, Mini DisplayPort doesn’t include audio, so to get sound when outputting to an HDTV using HDMI, you’d need to use yet another cable. This adapter uses USB for audio, so you get the full A/V with just one cable.