Kaki Hunter and Doni Kiffmeyer's "Honey House" in Moab, Utah. This is made of earthbags - sandbags filled with earth, tamped, and corbeled into a dome shape. Nader Khalili developed this way of building; Kaki and Doni (a couple of very cool people) are taking it to the masses. There's more photos of this structure (including construction shots), along with an article, at Pat Newberry's website.

Earthbag stem/retaining wall with exterior-pinned bales on top.