The Ultima Tower is a conceptualization by designer Eugene Tsui and it's built around alleviating city congestion in this increasingly congested world. It's debatably attractive shape is inspired by termite mounds and, instead of trying to brave the winds as your ordinary block-like skyscraper, it slopes gracefully to a point from a 7,000-foot-in-diameter base. The Ultima Tower is designed to provide good ol' self contained arcology living, takes advantage of renewable wind energy, has its own water supply at its base and throughout the tower, and uses reflecting mirrors to boost the amount of natural light throughout.
I wonder what construction firms think when they look at concepts like this? At least Tsui made it aerodynamic — it'd be a pain if it created some drag against the Earth's orbit.