Millenium Cell is a company that has been working on providing hydrogen based solutions for many things, including cars. Their sights have now targeted laptop computers. Though still in the development stage, a hydrogen cell for a laptop would be able to run for 12-14 hours per fill. I can foresee refueling points in airports and the like.
Sounds promising, as long as the whole refueling issue can be dealt with. Might get too expensive, though.