Jongerius Felt and Metal Stool
Designed by Hella Jongerius from the Netherlands in 2000 based on a beautiful ceramic version (see below). Made of low impact materials (felt and metal). The metal can easily be recycled and the felt can be composted. Bonus points if the metal used was recycled and if the felt was made from organic sources and used benign dies. I saw one for 300 Euros second-hand but am not sure where/if they sell them yet. ::JongeriusLab
The original white ceramic version.
A tiny shot of the hard to track down red version (which I bet is twice as cool).
Another shot of the blue stool.