iPod Shuffle (4th generation)
There is only one version of the Shuffle, and it comes with 2GB. The third generation still had a 4GB model, but now you're limited to 16 hours of 256 kbps mp3. That's longer than the 15 hour battery life Apple claims. Judging by our listening sessions that's not an unrealistic expectation. Assuming that each song has an average length of 4 minutes, you end up with 240 songs. Enough to not hear the same song twice right-away, but also not so much that you lose track without a display. Obviously the numbers are different when you increase or reduce quality and bit rates.
If you can get over the fact that you're paying a lot for very little storage, the Shuffle offers portable music in a package so light you'll quickly forget you're carrying it. With a weight of 12.5 grams you won't even notice it if you hang it from your ear, until the cable gets in the way.
The front consists entirely out of the control elements: fast-forward, reverse, play and pause, and the volume controls. The max volume is really loud, but in iTunes you can enable a limiter. One side of the player, let's call it the top side, has a 3.5 mm jack, a lock button, and the VoiceOver button.