How to Know the True BugsBy Slater, James A., and Baranowski, Richard M.
Wm. C. Brown Company, 1978
Part of the Pictured Key Nature Series. This one is, as of this writing (2004), out-of-print and hard to find. Very useful, in that it illustrates all families and many genera of hemiptera. Widespread or notable species are described in each genus. Almost 500 illustrations.
(This book should be under Heteroptera--not Pterygota.)