Hybrids - not so much
I just saw a fascinating posting that discusses the environmental impacts of hybrid vehicles. The posting refers to a 450 page report created by an Oregon research firm that looks at the environmental impact of a vehicle from 'Dust to Dust,' which means the total amount of energy consumed to create, operate, and recycle a vehicle.
As it turns out, the hybrid vehicles end up consuming more energy per mile once you factor in all the energy costs that go into producing and retiring the vehicles. I didn't have a chance to read the report, but I'm guessing a large factor is the manufacturing and recycling of batteries.
Another interesting tidbit is that the Hummer H3 costs less in energy per mile then the average vehicle sold in the US ($1.949/mile vs. $2.28/mile). I'd guess that the manufacturing techniques used in creating American cars contributes largely to this energy savings, as American cars tend to use universal parts. (Hummer parts are probably also found in other GM cars.) Often we look at the reuse of automotive parts as being a 'lack of refinement', but I suppose that could also be interpreted as an energy savings.
Overall I'd have to say the most energy conserving vehicle might be the one you're driving today. Every time you upgrade your vehicle, another vehicle gets sent to the junk yard, and another brand new vehicle is produced. Both processes consume a great deal of energy. So our 1997 Subaru Outback only gets 22 MPG compared to your 50 MPG hybrid, but at least the Subaru has been on the road for almost 10 years, meanwhile when you bought your hybrid, a vehicle somewhere got sent to the junkyard.