Online Resources:

General Information

American Society of Colon and Rectal Surgeons 
American Cancer Society
National Cancer Institute
Society for Surgery of the Alimentary Tract

Anorectal

Medline: Anorectal Disease
American Cancer Society: All About Anal Cancer
National Cancer Institute: Anal Cancer Home Page

Colon

www.colonoscopy.com
Medline: Colonoscopy
Cancer Care: Colon Cancer
Hereditary Colon Cancer Association
Center for Disease Control and Prevention: Colorectal Cancer Prevention
NIDDK: Diverticulitis
American Cancer Society: All About Colon and Rectum Cancer
National Cancer Institute: Colon and Rectal Cancer Homepage
Healthopedia.com: Colorectal Cancer

Endoscopy

American Society for Gastrointestinal Endoscopy: Patient Information 
NIH: Upper Endoscopy Information

Gastric Cancer

American Cancer Society: All About Gastrointestinal Tumors
National Cancer Institute: Gastric Cancer Home Page

Hemorrhoids

Merck Health Library: Hemorrhoids

Intestinal Health

Crohn's Colitis Foundation of America
Intestinal Disease Foundation
International Foundation for Functional Gastrointestinal Disorders
National Cancer Institute: Small Intestine Cancer Home Page

Obesity Surgery

American Society for Bariatric Surgery (ASBS)
American Obesity Association
NIDDK: Gastrointestinal Surgery for Severe Obesity

Pancreas

National Pancreas Foundation
American Cancer Society: All About Pancreatic Cancer
National Cancer Institute: Pancreatic Cancer Home Page