American Medical Association
American Society of Clinical Oncology (ASCO)
Colon Cancer Alliance "patient support, education, research and advocacy"
  (founded late 1998 by members of the ACOR Colon Cancer listserv)
Kimmell Cancer Center at Johns Hopkins
Lombardi Comprehensive Cancer Center (Georgetown University)

Mayo Clinic.com
- Cancer Center (information)

MD Anderson Cancer Center (University of Texas)

H. Lee Moffitt Cancer Center and Research Institute (University of South Florida)
- Moffit Cancer Center Cancer Control Journal (issues are themed, including cancer types, pain management etc.)

Memorial Sloan-Kettering Cancer Center (MSKCC)
- MSKCC locations
- MSKCC's list of cancer-related web resources

Sugarbaker Oncology Associates (Washington Cancer Institute, Washington Hospital Center, Washington, DC) "We specialize in the surgical treatment of cancers that arise in the gastrointestinal tract (appendix cancer, colon cancer, and rectal cancer), and other areas of the abdomen and pelvis. Our advanced services include specialty treatment programs for..."