Maxell announces a 10W hydrogen fuel cell based on water and aluminum.

The Maxell fuel cell measures 160×100×60mm and weighs 920g. 10W is not a whole lot, but a start.
As far as I can tell this fuel cell is just a milestone presentation from Maxell. They will continue to improve until the size and power ratio is becoming interesting for real world use.
More details in this Maxell press-release (Japanese). Via AkhibaraNews.

See also the Medis disposable Fuel Cell, which is supposed to hit stores this year.