Alternative Engine Technologies
Everyone is talking about alternative energy, hybrid cars, and other technological developments that can help reduce gasoline consumption. What are the technologies available? Let's make a list. I'll provide some of them below. I hope that some of you will add some additional technologies I'm missing in the comments.
Biodiesel (probably not able to scale large enough to replace much gasoline)
Ethanol (definitely not able to scale large enough to replace much gasoline)
Hydrogen (too expensive to produce and store at the moment)
Hybrid gas/electric (currently in use; price premium makes it unclear if they're a good deal, but that will improve)
Quasiturbine engines (not available yet, but R&D is ongoing: http://www.quasiturbine.com/ )
Camless engines (also not available, but Honda and other companies hope to release models without cams within four or five years.)
Rotary/Wankel engines (only Mazda uses them, and mostly for power/weight ratio. They're very efficient overall, but the focus has not been fuel efficiency. That could change! Mazda does have RX-8 hybrid rotary/hydrogen cars in Japan, but don't expect to see this in widespread production any time soon.)
Pure electric (Recharges from the grid. GM tried this, but gave up on it. It may not be practical, although it is probably a bit cleaner to generate power on a large scale and distribute it.)
So, what am I missing? What engine technologies are on the horizon, offering fuel efficiency and power gains? I could have listed small engines with turbochargers, or turbo diesels, but since those are not really new technologies, I'll leave them out.