Those of you interested in the development of Sonic Unleashed are going to like this info. 17 concept artwork pieces that were used in developing Sonic Unleashed were published to the internet recently by AOKIstudio's Geoffroy Thoorens. All 17 can be viewed by going to
http://www.djahalland.com/en/galerie/ and looking under Sonic Unleashed.
Source: TSSZ News, Sonic Stadium, Rings and Emeralds