The Oil Drum is a great blog. Originally more focused on peak oil, it now covers energy in general and is probably the best place on the net to learn and discuss these issues.
Today they have a look at some of our energy options for transportation, namely, Liquid Fossil Fuels, Grain Ethanol, Sugarcane Ethanol, Cellulosic Ethanol, Biodiesel, Biomass Gasification, Wind and Solar and Conservation. They use the following criteria:
1. Is the energy source sustainable?
2. What are the potential negative externalities of producing/using this energy source?
3. What is the energy returned on energy invested (EROEI)?
4. Is it affordable?
5. Are there better alternatives?
6. Are there other special considerations?
7. In summary, are the advantages of the source large enough to justify any negative consequences?
You can read the piece here: ::Key Questions on Energy Options.