I believe ULS (ultra low sulfur) diesel fuel either recently or will very soon be required in the US, so I'd imagine more diesel cars will begin to show up in the US.
I do not think hybrids are the answer, though. IMO we should be focusing on biofuels, i.e. biodiesel and ethanol. Diesels are very efficient, and according to what I've read, spark ignition engines designed for alcohols (that can take advantage of their higher octane rating, lower latent heat of vaporization, etc.) can achieve efficiencies similar to diesel.
Hydrogen is pointless at this juncture. The people that hype it up only tell part of the story. Sure it is clean, but currently there is no practical and efficient way to produce it. For now we are better off producing the energy directly in an engine, as opposed to burning fuel to produce electricity to produce hydrogen through hydrolysis to produce power through combustion. Just too many steps, very inefficient. Plus it would require replacing all our current infrastructure, whereas the move to biodiesel or ethanol would require little/no retooling for pumping stations, transportation, etc.