This product from from Bird-Electron is the “one and only Recycling Speaker for iPod”. The dimension is exactly the same as the plastic package for iPod Nano (1st & 2nd Gen.) and iPod Shuffle (2nd & 3rd Gen.).
It doesn’t require any power source whatsoever, you simply place the speaker panel on top of the open box, and plug it into the iPod and play. You can also create your own speaker by using a water bottle or any other small container.
The Bird-Electron EZ17-B iPod Recycling Speaker ($40) is available from AudioCubes.com for $39.99.