I recently came across the model from MAD which has a simple and artful facade. Construction is underway and is planned for completion in 2012.
From their website:
The varied honeycomb also improves the building's energy efficiency. Although the façade pattern appears random at first, it actually responds to the climatic conditions of the site. By mapping the different air-flows and solar direction across the site, and positioning the windows accordingly, it is possible to minimize heat loss in the winter and heat gain in the summer.
Sun and wind studies (above) which organized the shape of the hexagon facade.
The base of the tower
The skin is also structural, freeing up the interior from columns.
image credits MAD
