Im always interested in alternative energy..

agreed with above, the best way to save energy is conservation..
however there are more gadgets every year..

re cars:
I think there was a French car that works on compressed air..
It came out last year, dont know what happened to it.

there are hybrid plug-in electric cars right now, which essentially are converted hybrids with added lithium/ion battery banks (drawbacks are it increases weight by 170lbs, and invalidates your warranty on the other hand it can be plugged in and is sufficient for about 30km before kicking into gas engine mode) this would be an average daily commute so you could get quite a lot of mileage out of a tank of gas..
(of course it does require re-charging and uses electricity which still needs to be accounted for but typically that would be at offpeak hours)

Solar energy using mirrors focused on a sterling engine.
(Sterling Energy in California recently won a contract to supply
electricity - check out www.stirlingenergy.com) apparently it is still
the most efficient solar system - of course there are drawbacks too,
wind hail damage etc. but supposedly a 100square miles of their solar collectors would be enough to supply the total US electrical supply
-- quoted in Business Week article)

Recently Popular Mechanics had a few articles about alternative renewable energy-- and some good ideas were generating electricity from (chemical reaction with wasteprocessing plants) thus getting rid of poop and making energy - albeit it was a small amount - but enough to power a waste processing plant one day.

or small wind generators - even where wind is not high (average 11km per hour - but using a 5ft diam. windmill, which if the wind isnt high enough speed to recharge the batteries will store the charge as in a capacitor until there is enough to charge..

of course geothermal heat pumps..

using tidal power (floating grid of buoys using the up and down movement to induce electricity)

or tidal power in narrows, under water etc..

there is even a design for huge screens which would scrub c02 by having react with calcium and thus neutralizing it..
(i dont know why this cant be done on asmaller scale and simply attach it to car exhausts.. but Im not an engineer.)

cheers
Peter.