Identification, Images, & Information
For Insects, Spiders & Their Kin
For the United States & Canada
The Insects: An Outline of Entomology
By P. J. Gullan, P. S. Cranston
Blackwell Science, 2000
ISBN: 0-632-05343-7
Cite: 36806 with citation markup [cite:36806]
A good primer on general anatomy, physiology, and the discipline of Entomology as a whole.

I have the 2010 edition and would highly recommend it. It's very easy to read and provides great references.