iPod Shuffle, the little almost square ones.

So easy to operate all of the functions on it that it can be done without ever taking it out of your pocket. Navigate through playlists without having to look at it all. Battery life lasts seemingly forever. It made commuting by public transport in the cold so very much better than fiddling with the UI on a phone. And training meant not having to carry a huge and heavy phone when running because it clips onto your pockets-less training clothes somewhere.

Hands down the best designed device I have ever used.