Rather than try to explain the ins and outs of an earthbag house I'll just send you do an informative link. Then we can share why an earthbag house is one of our top preferences.
The Sandbag House
Our favorite things about the sandbag house:
1) We could do it ourselves.
2) Extremely Energy Efficient
The reason I call it an "earthbag" house is because the bags can be filled with the right material for your climate. If we consider this type of home more seriously we can discuss the type of medium we would choose to fill our bags with in more detail.
When Jake first presented this idea to me he asked what I thought about living in a round house. I said I would go crazy because rooms are supposed to be square, not irregularly half moon shaped or something. He then made a good point about how much more efficient it is in terms of heating the home. Although I'm not sold on it, I'm not completely against it because he does have a good point. It's nice to know that Sandbag houses don't have to be round.
This is just one option, but seems to be our favorite at this point.