Episode, number three covered the types of fuels that we are likely to see in the coming years. All of the usual suspects were included: ethanol, biodiesel, hybrids, pure electrics, hydrogen, solar and even compressed air were all considered, and got roughly equal coverage. Left off the list were biobutanol or any of the other bioalcohol-based fuels.
Linton, a frequent poster on Hugg, has posted his summary of each episode, and here is a link to his coverage of the third. I also noticed that the show incorrectly referred to the air-powered car as perpetual motion.
[Source: AutoblogGreen Future Cars on Discovery highlights fuels of the future]