Yes, "Edible Leaves of the Tropics" is great.
ECHO's bookstore is perhaps the best place to find books on this subject, including the above.
Other good reads on vegetables:
"Tropical Leaf Vegetables in Human Nutrition", by H.A.P.C. Oomen and G.J.H. Grubben, Royal Tropical Institute, Amsterdam, 1978.
"Manual of Minor Vegetables", by James M. Stephens, Florida Cooperative Extension Service-IFAS, June 1988.
"Unusual Vegetables", ["79 vegetables you can grow when you're tired of tomatoes, bored with beans, and sick of squash"] by editors of Organic Gardening and Organic Farming, Rodale Press, 1978.
Also good, but extremely dry, reading--- to look up something in when you have already noticed that something looks tasty but you don't know if it is OK to eat:
"Vegetables in the Tropics", by H.D.Tindall, Macmillan Press, London, 1983.
ECHO's Inventory of Tropical Vegetables", by Franklin W. Martin, E. victor Doku, and Ruth M. Ruberte.
"Cornucopia II: A Source Book of Edible Plants", by Stephen Facciola, Kampong Press, Vista, California, 1998.
In Portuguese:
"Hortalicas Nao-Convencionais da Amazonia", by Marinice Oliveira Cardoso et al, EMBRAPA, Brasilia, 1997.