The Society for the Advancement of Women's Health Research is the only national advocacy group whose sole mission is to improve the health of women through research. This nonprofit organization, founded in 1990, brought national attention to the problems of excluding women from major medical research studies. The Journal of the American Medical Association which contains a Women's Health Information Center site has some very useful information. You can search through current or archives of JAMA for abstracts on women's health issues. Breast Cancer Information for Patients, Caregivers and Health Professionals is a selected list of sites slanted towards information of interest to breast cancer patients and caregivers, including resources on clinical trials, support groups, survivorship, therapy, diagnosis, statistics and risk factors.
Many sites have full text materials both in English and Spanish.