American Cancer Society
CancerGuide (Steven Dunn's Cancer Information Page
CancerWeb Multimedia information resource for oncology, based in the UK.  Their objectives are:1. Provision of information about cancer for clinicians and patients.
2. Educational resource site for health care professionals. 3. Communication between trainees in oncology. 4. Collection of information relevant to oncology. 5. Development of information systems and means of distribution.
The National Alliance of Breast Cancer Organization
National Cancer Institute Federal Government's principal agency for cancer research and training, information dissemination,  assess the incorporation of state-of-the-art cancer treatments into clinical practice
National Coalition for Cancer Survivorship
Oncolink - Cancer Center of the University of PA
PERC Pathways - Information guides (PERC Pathways) - lists of information sources relating to a specific cancer diagnosis or issue.  Provides a starting point for gathering information.  University of Michigan Comprehensive Cancer Center.
Susan G. Komen Breast Cancer Foundation
Your Cancer Risk Harvard Center for Cancer Prevention.  Estimates your risk of cancer and provides prevention tips.