According to Clean Energy Canada with regard to fuel cells, "Current projections anticipate an industry growth rate of 75% per year over the next decade, for an expected worldwide commercial market of $46 billion in 2011."
Clean Energy CA

Please note that this is their estimate and other market estimates may or may not support this one.

Part of the reason they expect such quick growth and such a substantial market share is that fuel cells are cleaner and more efficient than combustion engines, they are mechanically sound due to limited moving parts, multiple fuels for powering (hydrogen, natural gas, methanol, and gasoline), low emission, and multiple application ranging from individual use to industry use.

Typically, fuel cells can be categorized into three categories:
Stationary Fuel Cells
Portable Fuel Cells
Transportation Fuel Cells

Presently, stationary fuel cells are used in backup power applications. In the near future stationary fuel cell application will range from small units designed to power individual residential homes to large units formed in groups to be used as a power plant.

Portable fuel cells have similar application to stationary cells except that as the name describes they are portable...

Transportation fuel cells are presently in the development stage with some prototypes in operation at this point. As for generally accepted use in personal vehicles the cost of the technology will have to come down substantially. Some car manufactures are predicting a 30 year gap before any wide spread personal fuel cell transportation use. The present market estimate for trans-cells is small but significant at about $100 million dollars.

According to a report put out by NAVC: "The automotive manufacturing companies offered differing opinions about the progress of the technology (transportation fuel cells). One company was very enthusiastic about the progress of technical developments. As this representative put it, "in comparison to the progress made in battery technology during the 80's and early 90's, fuel cells are showing a significantly faster rate of development." On the other hand, another company said they were disappointed with the incremental progress over the last few years."