American Stonefly
Dr. Bill Stark provides links to images of many North American stoneflies.

Dragonflies and Damselflies
Not specifically for anglers, however this site has a good amount of information for anyone wanting to learn more about entomology.

Dragonfly Site
Dragonfly biology and links.

Flyfishing Entomology
Fly fishing entomology. Excellent resource. Provides comprehensive aquatic insect information not otherwise centrally available. Included are such instructional topics as zoological classification, taxonomic structure, metamorphosis, and anatomy.

North America Stonefly List
Dr. Bill Stark's data base of stoneflies of North America including geographical distribution by state and province.

Phenological Fly
Bob Scammell's method for matching the hatch. (Book Review)

The Ephemeroptera
An interesting site providing lots of information on the life cycle of Mayflies.

Troutnut.com
Troutnut.com gives an unprecedented look at the wide array of fascinating creatures, large and small, that dwell beneath the surface of even our smallest streams. It includes over a thousand closeup pictures and videos of stream creatures, as well as many underwater photos of trout and stream insects in their natural habitat. A really cool site! I'll spend some hours here.