The problem with ethanol is it doesn't have enough energy per unit volume and is expensive to produce.
If every single acre of current and future farmable land were converted to growing corn for ethanol use, it would only yield something like 30 percent of our vehicle fuel needs in the US. Then we'd have to buy food from somewhere else. This info comes from popular mechanics, not from my noggin. I'm not 100% sure on the percentage, but I'll try and remember to look it up and repost if I am way wrong. I do remember that it didn't produce nearly enough fuel.
They can produce ethanol from cellulose fibers (ie wood chips, grass, and other waste products) but again, it is expensive to produce.
I like biodiesel - i bought an old mercedes diesel wagon to convert to either bio or veggie oil. Diesel engines are much more efficient in terms of MPG, so I think a full on conversion to more diesel engines is a first step to reducing our oil dependancy by increasing our per capita mpg. Honda and Mercedes are developing engines that will meet the stringent new CARB guidelines to reduce NOx emissions, so the pollution shouldn't be any worse than gasoline. I think they actually produced less CO2, but I'm not sure. I also don't know what the costs are associated with producing biodiesel vs. ethanol, but if they are anywhere close, biodiesel would win out because of the greater mpg the car with the diesel engine gets.
I don't think fuel cells will ever turn into anything as there are costs associated with producing the hydrogen.
I think that the best bet for our future is electric vehicles. Electricity can be produced with solar energy, wind energy, hydroelectric energy, and nuclear power, along with the standard coal, natural gas, and fuel oil. The price of photovoltaic cells is coming down everyday, and if everyone installed these on your roof, you'd have enough free energy to light your house and run you car. If they can improve battery technology to a point where the batteries will last say 15 years before they lose their charging capacity I think somebody would be in business.
I'm not a hippie or environmentalist persay, but I would like our country to be energy independent, and would like to not have to buy dern gasoline anymore!! Plus I just had a child and would like this world to clean up some so he won't be breathing in crap when he's my age.
Just my 2cents!