WIRED published an annotated slideshow of small prefabs last week:

The world is getting hotter and more crowded every day, and modular, prefab housing is just what the doctor ordered. When you go small, it's not just about energy efficiency and carbon footprints -- it's also about being strange, cool and beautiful. We've chosen our favorite houses that meld style with globally conscious living. Enjoy.

Models included:
•  weeHouse
•  Modern Cabana
•  Marmol Radziner Prefab
•  micro compact home

Treehugger summarized:

Some are real and some are vaporware; all have been around the block a few times. And of course, the comments include "why are these so expensive?"