Not to bore everyone with what interests me at the moment, but I just spent most of the evening reading about oxyhydrogen generators you can build at home or buy off the shelf, install in your car, and increase your fuel economy by 25 to 50%. It converts water (HOH) into "Brown's Gas" (oxyhydrogen, HHO). This oxyhydrogen on demand makes your fuel burn more efficiently and gives your engine more power. Now that gasoline prices exceed $3.33 per gallon, this seems worthwhile.
For this invention to be completely carbon neutral, you'd have to add another battery to your car and add solar panels to charge it. Otherwise, you're using power from your alternator. But, my understanding is that the alternator makes much more electricity than is needed to charge your battery and the field current which is allowed to pass the regulator is based on feedback voltage from the battery, so the battery only gets juice when it needs it, so using this energy to make an oxyhydrogen additive is gainful because it's otherwise wasted. Furthermore, the expense of installing the system is tax deductible.
Here are some plans for making an HHO generator out of some #80 CPVC pipe and concentric stainless steel exhaust pipes with a 1mm gap. These pipes are the diodes and electricity is pulsed at a frequency you can tweak for the best HHO to fuel mixture for your particular engine. http://www.spiritofmaat.com/archive/feb2/carplans_doc.htm
On YouTube, I've seen pure HHO lawnmowers and cars, so using water plus a pinch of baking soda for fuel with an electrical assist to convert it to HHO is a viable emerging technology.