Reddit reviews Human Creations Bicycle Dynamo USB Charger Kit with Universal Phone/GPS/iPhone/MP3 Holder

http://www.amazon.com/Human-Creations-Bicycle-Charger-Universal/dp/B008KET1V2

This is really cool. I love making things and tinkering so I'd usually take on a project like this, however it seems that the cost with all parts/tools necessary would push it past the cost of a retail product. That plus my time kind of makes it less practical.

For anyone wanting to see a retail option, I found this cell phone charger, including universal mount, on Amazon. The nice thing about it is that the USB cable is not hard wired, so you can easily plug in a micro, mini, or Apple type USB cable for use with multiple devices.

You're looking for a bicycle dynamo. A quick search should lead you in the right direction.

http://www.seeedstudio.com/depot/Bicycle-Dynamo-With-Bracket-6V-3W-p-798.html?cPath=1

EDIT

Something a little easier and more straightforward

EDIT2

This isn't /r/bicycles.

EDIT3

There are 12v outlets that attach directly to the battery, which you could attach a car charger. I don't know about going directly to 5v though.

[Google search for "bicycle dynamo usb" and this was the first link] (http://www.amazon.com/Human-Creations-Bicycle-Charger-Universal/dp/B008KET1V2)