Recyclable? Check. Minimalistic? Check. Cheap? Check. The eco-amp from a new design company called eco-made hits all the highlights for an environmentally-conscious iPhone accessory. "Accessory" in this case mostly means "cardboard and adhesive," as the eco-amp is nothing more than a foldable amplifier for the iPhone's little bitty speakers.
The amp slides over the bottom of the iPhone (leaving a convenient space open for the home button) and will give your music a slight decibel boost, so long as the amplifier cone is pointed at your head. An $8 pack includes two eco-amps, but tack on shipping and taxes and you're looking at about $15 for a papercraft amplifier.
The idea's solid, but $15 is a little steep for some DIY papercraft. If you already have some heavy paper stock lying around, try out the free Boostie Boy template first. It'll only cost you a few cents in paper, ink and glue. And you'll still be environmentally friendly.