If you struggle to be in tune due to tone deafness, or any other reason then an eNote Digital Tuner would be ideal. You attach the clip to a guitar and pluck away till the display turns green. This indicates that you are now in tune. Not only will it tune guitars, it will also work with any other string instrument too. It costs $25 and is available from ELECA.
Via: SlipperyBrick and GadgetTastic