Good (IMO) blog discussing alternative energy sources:
Linky
His conclusion is that the only energy sources which are even remotely practical with current engineering and are scaleable enough to make a dent in the USA's fossil fuel usage are nuclear fission and (maybe) geothermal.
The author might have an agenda, but why not read his work anyhow? Raises some points about the "popular" alternatives (e.g. bio-fuels) and the flaws that get so easily glossed over (like scaleability).