I have a book called Foraging New england, that I also blogged. The idea is a great one-instead of listing literally hundreds of plants, it goes over the most commonly found ones in any given area-and its preparation and uses. This is the best guide I have found so far. I dont know if they do guides for every region, but the one for mine is nice-I have learned most of the ones in my local area in just a few weekends.