Beneficial Insect Sites
The following two Web sites are very useful as guides to beneficial insects and how they can help you garden more successfully. Check out:
Biological Control: A Guide to Natural Enemies in North America
Biological Control Virtual Information Center
Natural Enemies Handbook: The Illustrated Guide to Biological Pest Control
My absolute favorite reference book on natural enemies is Natural Enemies Handbook: The Illustrated Guide to Biological Pest Control, by Mary Louise Flint and Steve H. Dreistadt (University of California Press, Publication 3386, 1998; $35 softcover, $50 hardcover). It offers a multitude of useful photos, charts, and diagrams, and the text is full of useful information to help you learn about managing the "good guys" in your garden.