Asian cuisines have long incorporated Black Garlic, but only more recently has this fermented version of the bulb been commercially available in the U.S. and Britain. Eaten as a snack or used as an ingredient in cooking, it boasts a vinegary sweet flavor and health benefits.
After fermenting in clay containers for a month—with no additional ingredients added—the result is a mellower-tasting clove with ten times the antioxidants of raw garlic. The aging process also creates S-Arylcysteine, which has purported health benefits as a cancer- and cholesterol-fighter, and increases polyphenol content. While this sounds like something that would make the garlic smell like a hundred year egg, the smell is actually quite pleasant and not intense at all.
A quick search shows that black garlic is showing up on menus at Bix, Charlie Trotter, Monarch and Le Bernadin, as well as on shows like Top Chef.
Black Garlic is currently available from some retail locations in the San Francisco Bay Area, online from Mondo Food (starting at about $4 per bulb) and from the Black Garlic site directly in the U.K., which also carries black garlic paste and juice.
Read more about Black Garlic on Wikipedia.