Alternatives to fossil fuels are pretty well known, but it's hard to beat the short term returns from burning hydrocarbons that are pumped out of the ground -- which is why fossil fuels still make up about 80% of our energy supply. One of the most environmentally-friendly energy sources comes from wind turning some turbines to generate electricity, and wind power has been growing rapidly in the last few years. In 2010, wind power generated about 2.5% of worldwide electricity usage (about 430 TWh), up from just 0.1% in 1997 and projected to hit 8% by 2018. If you're interested in the creation of energy out of thin air, here are just a few links to check out.
If you'd like to read more awesome and interesting stuff, check out this unrelated (but not entirely random!) Techdirt post