Depends on where you are. For North America, I don't think there's a better book than "The Encyclopedia of Edible Plants of North America" by Francois Couplan with the foreword by Dr. James A. Duke. http://books.google.com/books?id=tb_qBpULHKcC&dq=&pg=PP1&ots=_Chhnz_pmH&sig=m2C8Z_5HOdxOKnI9FYYC1g6jb9U&prev=http://www.google.com/search%3Fas_q%3D%26hl%3Den%26num%3D10%26btnG%3DGoogle%2BSearch%26as_epq%3Dedible%2Bplants%2Bof%2Bnorth%2Bamerica%26as_oq%3D%26as_eq%3D%26lr%3D%26as_ft%3Di%26as_filetype%3D%26as_qdr%3Dall%26as_nlo%3D%26as_nhi%3D%26as_occt%3Dany%26as_dt%3Di%26as_sitesearch%3D%26as_rights%3D%26safe%3Dimages&sa=X&oi=print&ct=title#PPP7,M1 http://www.amazon.com/Encyclopedia-Edible-Plants-North-America/dp/0879838213 Peace, poor_old_dad
'From Agar to Zenry' by Ron Freethy. The author started foraging with his great-grandmother whom people nicknamed 'the little witch'. Goes into great detail about plants, gathering, storage and uses, medicinal, culinary and industrial, even touches on folklore. Good read!
I dont know if this will apply to you, because I dont know where you are from, but i have this book called "Missouri wild edibles" and it is very detailed, and has ways to eat all kinds of stuff, plus pictures for each plant. It tells when they are available, what kind of area they grow in etc.
