For the short term, I like methanol. Current gasoline-powered cars can be converted to burn it without too much pain, and there is a new type fuel cell (the DMFC -- direct methanol fuel cell) which can convert it directly to electricity for electric cars. It can be produced from almost any source of carbon (natural gas, coal, garbage, agricultural product waste, etc., etc.),and can be stored and distributed using the same system for gasoline that we already have in place.
I think the long-term ultimate answer is a photovoltaic+nuclear+hydrogen economy.