Glacier architecture
Strictly speaking, ice isn't organic. But the forms taken by frozen water are among the least linear geometric shapes, in particular the glacier - a frozen river-mountain.
Rome architect Massimiliano Fuksas' New Milan Trade Fair (2002-2005) may be a building with an incredibly unromantic name, but the sweeping canopy which acts as a flowing sister to the alp-lined horizon is one of the most beautiful roofs imaginable.
There's an article and photo here.
Link to the Massimiliano Fuksas site.