Gadget Metro

This one is awesome. The author has an excellect documentation on how *SHE* did it from conceptualizing, to design, to prototype creation, then to kit production. She even discussed computations on efficiency of the charger. You can even follow her thought process on how she choose the parts to be used, and even details costings.

The resulting USB charger uses an altoids tin casing and it can charge mp3 player, ipod, pda, any device that can power from a USB port.
For all DIY people, you gotta see this.

[via instructables ]