Some governmental or professional medical search engines are directed at health professionals and scientists, but with some careful reading, we "civilians" can glean what is needed in most cases.
PubMed: The National Library of Medicine
PubMed lets you search more than 16 million bibliographic citations and abstracts in the fields of medicine, nursing, dentistry, veterinary medicine, the health care system, and preclinical sciences. It provides access to MEDLINE® and to articles in selected life sciences journals not included in MEDLINE. PubMed is a free resource. It was developed and maintained by the National Center for Biotechnology Information (NCBI) at the U.S. National Library of Medicine (NLM) located at the National Institutes of Health.
PubMed Quick Start Tutorials
This is an excellent overview of how to use PubMed and includes a link for a short video presentation. There are extensive links for additional instruction. A great starting point in your search.
PubMed Animated Tutorials
A list of all the videos available on most aspects of searching on PubMed.
CAM on PubMed
If you're mainly interested in CAM (complementary & alternative medicine) options, then this is the place to start. NCCAM and the National Library of Medicine (NLM) have partnered to create CAM on PubMed, a subset of NLM's PubMed. Your free literature search will be automatically limited to the complementary and alternative medicine (CAM) subset of PubMed.
MedlinePlus
www.medlineplus.gov
A vast searchable database that will direct you to information to help answer health questions. MedlinePlus brings together authoritative information from National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations. Preformulated MEDLINE searches are included in MedlinePlus and give easy access to medical journal articles. MedlinePlus also has extensive information about drugs, an illustrated medical encyclopedia, interactive patient tutorials, and latest health news. It contains extensive health information from the world's largest medical library, the National Library of Medicine.
MedlinePlus has extensive information from the National Institutes of Health and other sources on over 700 diseases and conditions. There are also lists of hospitals and physicians, a medical encyclopedia and a medical dictionary, health information in Spanish, extensive information on prescription and nonprescription drugs, health information from the media, and links to thousands of clinical trials. MedlinePlus is updated daily and there is no advertising on this site, nor does MedlinePlus endorse any company or product.
MedScape
www.medscape.com
One of the largest collections of professional medical information on the internet from WebMD. Keep up to date on the latest developments in your medical area of interest. Medscape has daily medical news updates you can subscribe to if interested.
http://www.niams.nih.gov/hi/topics/howto/howto.htm
Although this is not a cancer-related website, it gives some excellent information about searching for health-related information in general.
Searching on Google
http://www.google.com/support/bin/topic.py?topic=352
Not health-specific, but there are links here for how to do basic and advanced searches on this global search engine.