I've been reading about the Rocky Mountain Institute recently and how their energy efficient design going back to the 80s cuts their heating cost to almost $0. We're up in the mountains this weekend and it's close to zero degrees outside. The house we're staying in is fully heated and warm inside thanks to propane gas heating. This house doesn't have air-conditioning because the summers here are mild and the fresh mountain air and the breeze is enough to cool the house on a hot summer day. The orientation of the house faces the south, so it's already suited to receive the sun's heat from mid-day till the mid-afternoon to collect the heat.
Take a photo tour of the Rocky Mountain Institute building.
And here's an article from MSN about these green buildings.