OK, this is stretching it. But if you're seriously considering a greener lifestyle, then check out the iFan. It's really just a modified PC fan molded into a rubberized iPhone case. The catch is you'll need to strap this onto a bicycle (and we're not talking a stationary bike here) to generate the kind of breeze needed to get this charger going.
Designer Tjeerd Veenhoven says it takes him roughly six hours to fully juice his iPhone using the iFan, which equates to an equivalent amount of time working those leg muscles. So cross your fingers Veenhoven gets kicking on redesigning the blades to speed up the charging process. Else sustainability be damned, we'd be the ones requiring sustenance.