Panasonic's latest fuel cell breakthrough is the world's smallest designed for notebooks—270cc, about the same size as the existing lithium ones. They use highly concentrated methanol, similar to ones designed for the military as the fuel source, though 200cc of juice will give you 20 hours of power—or a whole one with an Alienware full SLI monster playing Crysis at max settings.
They've also got a paperback-sized one that'll charge gadgets. Both are supposed to be commercially available in 2012, though we won't believe we can carry around tanks of methanol laptop power until we actually do it. [Panasonic (Google Translated) via Crunchgear]