ZBMAN and senoir Martin
H2 has to be produced and at present that's using normal Fossil Fuel or Nuclear power - so a hydrogen economy is still a long way off. In addition the infrastructure would need changing significantly for cars to run on H2.
Bio fuels are a reality and not a dead end - yes it's true that in certain climates the likes of oil seed rape etc are unlikely to reap benefits of production cost (environmental as well as financial) - however take Miscanthus (better known as Elephant grass) as an example - it actually creates it's own compost so you don't need fertilisers and so less machinery/CO2 emissions. It grows far better in Africa than the UK (funny that - maybe why it's called Elephant grass then!) - there it can be grown when Maize is out of season and used to improve food crop yields in season.
www.nrfd.co.uk has some good links to papers on these fuels. There's no reason they can't be developed for gas turbines.
Bio diesel can be used in just about any diesel car - at present it's blended 5-10% with normal diesel. Chip fat can be turned into car fuel but you need a pre heater in winter and beware the fishy smells!
Ethanol blended with normal petrol has significant octane benefits and lowers emssions. The latest blends don't corrode away the internals like the 1970s brasilian variety. Expect to see it used in forthcoming F1 cars soon.
Another way to save fuel is to use ground effect - remove your induced drag entirely by flying very low over the sea - not in a 747 but a specially developed ekranoplan / WIGEC vehicle.