We've just completed a remodel of our house and much of what we did was related to energy conservation like improved insulation, dual pane windows, more efficient lighting, and on demand water heating. It's a little too early to tell, but if the preliminary results hold up, we've reduced our energy needs by at least 28%.
I've heard mixed results about the "on demand" heaters, so it will be interesting to hear how you think it goes.
One thing I've shied away from is the high efficiency ( > 92% ) furnaces. Everyone I have talked to, including several HVAC installers, say that between the additional up front cost and the sky high repair cost when they break there is no real savings. Because they are 10x more complex, they also tend to break much more frequently.

:p
