http://www.cdc.gov/ Centers for Disease Control. Complements Medline Plus. Has an up-to-date compilation of late-breaking news from medicine, without a spin, just facts.
http://www.mayoclinic.org/, Mayo Clinic. Content tends to be academic but very detailed and well researched. Good online search engine.
http://www.drugs.com/ Fairly comprehensive and up-to-date source of drug information online. Free, peer-reviewed, accurate and independent data on most prescription drugs, over-the-counter medicines & natural products.