I've recently found a fantastic prefab house system from Tallman Koch, an architecture firm in Los Angeles.
They have developed a building system which allows quick on-site assembly of steel panels with no need for heavy machinery. The structure is built around standard sizes of cabinets, windows, etc. This provides flexibility and cost efficiency.
cabin, which reminds me of our own little stuga in a way, especially in this photo to the right. Fuller-size houses are also available.
The website is full of information about their buildings and the construction process. Of course, they are ecologically friendly, too, with various innovations in solar energy, passive heating/cooling, and water reclamation available.
They also remind me of the Case Study homes built a half-century ago in Southern California: efficient, simple, open, steel and glass structures. I like these very much!