In reply to iusedtoclimb:
Use an old car not a new one (Most energy goes into making new).
It's interesting that focusing on cost, tends to result in the reduction of Co2. Air travel is probably one of the big ones, where cost and Co2 production are not reflected in one another.
We have solar panels making electrickery, and because I can't get FIT payment on a second set, I'm just (this summer) wiring a second smaller set directly into the immersion heater, to provide summer hot water. (That may not be for everyone).
Concrete is a big Co2 generator, so a low level of concrete use will help. Natural lime will do about the same job, and sometimes better depending on circumstances.
What about grass clippings - is there much benefit in not cutting lawns (Oh I'm all for that), or considering how we deal with the clippings it produces. We tend to compost ours, or leave on the lawn after the first cut of the season.
Oh, and washing machines, dishwashers etc on at night. It tends to reduce demand on the diesel generators brought in on standby. (No cost benefit though).