Trametes versicolor is a wood-eating shelf fungus who can be found year-round in much of North America. It's common to find large logs covered with hundreds of these hairy, leathery fruiting bodies. (Michael Kuo's article covers how to separate this species from similar fungi.) The top colors vary widely but often include blues, browns, and creams; the outer margin is usually white. On the underside of these multi-colored shelves is a white or nearly white pore surface with thousands of tiny openings. This species is commonly known as Turkey Tail.
Greg Marley writes at length on the medicinal properties of T. versicolor (or extracts thereof) in his book Mushrooms for Health: Medicinal secrets of northeastern fungi (2009) and reports that, "Turkey Tail is the best-researched and most clinically tested of the medicinal mushrooms, at least by allopathic medicine standards" (p. 82). A formulation of Turkey Tail known as PSK is a leading anticancer medicine in Japan, often prescribed in combination with radiation and chemotherapy. (Read Marley's chapter for more details.)
Turkey Tail is too leathery to be consumed in whole form, but fungi foragers can prepare hot water decoctions (broths) and/or double-extraction tinctures of this mushroom. Just be sure to gather only actively growing mushrooms, with white growing edges and fresh pore surfaces. (To view the following images in full-size, click here.)