American Botanical Council  is an independent, nonprofit organization that provides education to promote the responsible use of herbal medicine. The site reports on the latest clinical trials and other published research and offers information on individual botanicals. Some of the information is only available to members. Membership is well worth while, particularly at the "academic" level ($100 per year for U.S. residents, $120 per year outside the U.S.). Membership at this level provides access to a number of useful resources, one of which (HerbclipTM) provides comprehensive reviews of the latest publications about botanical medicines in peer-reviewed journals.
Center for Food Safety and Applied Nutrition Dietary Supplement  answers questions about how the government regulates botanicals and posts recent safety alerts.
Dietary Supplement Information Bureau  is a project of the Dietary Supplement Education Alliance, a partnership of scientists, educators, and industry professionals that was created to promote the responsible use of vitamins, minerals, herbs, and specialty supplements. It contains an A-Z reference for the use of vitamins and herbal remedies, as well as a health concerns index that suggests botanicals for specific conditions.
HerbMed  is an online herbal database that provides access to the scientific data underlying the use of herbs for health. This public site provides free access to 45 herbs (top 40+ controversial herbs).
Medline Plus  offers a free A-Z reference on herbs and supplements from Natural Standard, a respected non-profit scholarly source. This site rates evidence for each intended use of a botanical, gives recommended dosage, lists safety considerations (including possible interactions), and lists selected references.
NCCAM  is the National Center for Complementary and Alternative Medicine. Its website includes articles about specific botanicals.
NSF International  is an independent, not-for-profit organization, committed to making the world a safer place for consumers by testing and certifying dietary supplements. The site allows you to search a particular brand of botanicals to see if it is in the NSF database of certified dietary supplements.
PubMed , also known as Medline, is the primary database for peer-reviewed publications in the biomedical and life sciences. Both Medline Plus and Pubmed are administered by the National Library of Medicine.
United States Pharmacopeia  is a non-profit association evaluates botanical manufacturers' processes and products. The site includes a list of manufacturers (and brands) that participate in the USP evaluation program, as well as a list of stores where the certified products can be purchased.
Chevallier, A., Emerson-Roberts, G. (2000). Encyclopedia of Herbal Medicine: The Definitive Home Reference Guide to 550 Key Herbs with all their Uses as Remedies for Common Ailments. DK Adult.
Duke, J. (2000). The Green Pharmacy Herbal Handbook: Your Comprehensive Reference to the Best Herbs for Healing. Rodale.
Basch, E.M., Ulbricht, C.E. (Eds.) (2005). Herb and Supplement Handbook. The Clinical Bottom Line. Elsevier Mosby.
Blumenthal, M., et al., (Eds.) (2003). ABC Clinical Guide to Herbs. Theime Medical Publishers.
Brinker, F. J. (2001). Herb Contraindications and Drug Interactions, Third Edition. Eclectic Medical Publications.
Lewis, W.H. and Elvin-Lewis, M. (2003). Medical Botany: Plants Affecting Human Health, 2nd ed. John Wiley & Sons.
McGuffin, M., Hobbs, C., Upton, R. & Goldberg, A. (1997). Botanical Safety Handbook. CRC Press.
McKenna, D.J., Hughes, K., Jones, K. (Eds.) (2002). Botanical Medicines: The Desk Reference to Major Herbal Supplements, Second Edition. Haworth Herbal Press.
Mills, S., Bone, K. (2000). Principles and Practice of Phytotherapy. Churchill Livingstone.
Mills, S., Bone, K. (2005).The Essential Guide to Herbal Safety. Churchill Livingstone.
Schulz, V., Hänsel, R., Blumenthal, M., Tyler, V.E., et al. (2004). Rational Phytotherapy: A Reference Guide for Physicians and Pharmacists, Fifth Edition. Springer.
Upton, R. (1994-2005). Monographs of the American Herbal Pharmacopoeia (ongoing, by plant species). To purchase: http://www.herbal-ahp.org .