This iGo keychain fob sized USB smartphone charging cable is fantastic! It is compact, flat and simply gets the job done.
I work outside of the house quite a bit and keeping a smartphone charged is a total pain. Remembering to bring the right cable for the right gadgets, external chargers or what-have-you is always a problem. This iGo pocket-sized USB micro and mini cable solves this. The iGo is also sturdy. I've had problems with other, slightly cheaper models falling apart in a matter of weeks.
iGo KeyJuice Charger for Smartphones – USB to Micro and Mini USB