American Association of Family Physicians: A one-stop resource featuring a wealth of information on the disease along with related resources.
The Mayo Clinic: Provides a comprehensive overview of the condition along with multimedia, expert answers, and links to other condition-related resources
Medline Plus (NIH): A good overview including diagnosis, treatment options, nutrition, and coping with the disease to name a few. Provides good links to external resources as well.
National Digestive Diseases Information Clearinghouse: A good resource that provides general celiac-related information along with treatment and diet recommendations.
WebMD: A thorough resource (CeliacDisease Health Center) providing everything from symptoms and diagnosis to learning to live with the disease and also tips for eating with Celiac disease.