Wikipedia: Woodpecker – General characteristics, distribution, habitat and movements, behavior: diet and feeding, breeding, and systematic evolution.
All About Birds: Woodpeckers and Allies – Site includes the following info – A variety of woodpeckers, their identification, life history, and a sample of the sounds they make. Some videos have been included for some of the woodpeckers as well.
Defenders: Woodpeckers: Basic Facts – Info includes – Diet, population, range, behavior, reproduction, and protection status.
Smithsonian National Museum of Natural History: Article:
Woodpecker Images in the Late Prehistoric Southeast
FranW.com: Bird Watching Activities – Offers a variety of ideas for bringing birds to your yard.