Plants for a Future
Plants for a Future is a resource center based in England whose online database provides extensive details on the edible, medicinal, and other uses of over 7,000 plants, plus information about their cultivation and habitats.
The center also keeps a research and demonstration garden on organic permaculture in an ecologically sustainable environment in Devon, England, and offers a number of leaflets on plant use and useful plants.
Handbook of Edible Weeds
For factual information on edible weeds, including description, distribution, and utility, check out the Handbook of Edible Weeds by James A. Duke (CRC Press, 1992; $50). For enticing photos and recipes with weeds, consider The Wild Food Gourmet by Anne Gardon (Firefly Books, 1998; $25).