A round house on a private island in Mamaroneck, NY, is now on sale for $2.595 million (down from its original asking price of $3.1 million) –
This swirling video shows the circular dwelling from the air.
Back in 1962, when the house was under construction, it caused something of a sensation. The New York Times published a front page article that described the house’s layout and architectural elements in detail. Designed by the firm of Harsen, Johns, Kobayashi & Fermery, the house is 65 feet in diameter and cost $50,000 to build.
round houses 
Update: the house just sold for $1.6 million — http://www.randrealty.com/NY/Property/1571241/1130-Cove-Island-Mamaroneck-NY-10543/.