National Cancer Institute (NCI)
Authoritative, detailed information and search mechanism for cancer clinical trials nationwide
"Introduction to Clinical Trials"
The basics on clinical trials, also from the NCI
Helpful resources, including a podcast, from the American Society of Clinical Oncology
Nationwide matching service for individuals diagnosed with or at risk for breast cancer, developed by UCSF
Registry of all clinical trials — for cancer and other medical conditions — from the National Institutes of Health (NIH)