Wikipedia - Beetles
http://en.wikipedia.org/wiki/Beetle
An online encyclopedia with great general information on beetle anatomy, biology and classification.

The Coleopterists Society
http://www.coleopsoc.org
The official site of the international professional society devoted to beetles.

Field Guide to California Beetles
http://www.sbnature.org/calbeetles/fieldguidesuppl
This site (hosted at SBMNH) offers supplementary information and images for Art Evans and Jim Hogue's recently published field guide (available from the University of California Press).

Beetles in the Tree of Life
http://tolweb.org/Coleoptera
Explore what we know about the beetle branch of the tree of life so far. Includes discussion of characters of major beetle groups, their evolutionary history, and many photographs.

The Beetle Tree of Life Project
http://insects.oeb.harvard.edu/ATOL/index.htm
Site showcasing an NSF-funded collaboration to resolve evolutionary relationships among all major groups of beetles.

Museum of Comparative Zoology (Harvard) type database
http://mcz-28168.oeb.harvard.edu/mcz/index.htm
Searchable database with photographs and data from Harvard's rich beetle collection, including the types of LeConte, Horn, Fall, and others.