Research 1 Herb
RxList This is the best site for fast access to interactions, side effects, and contraindications, matters of tremendous import for case analysis of the patient who is taking prescription drugs. Search by generic or trade name.
U.S. Pharmacopoeia. Not much useful information here, but contains a guide to products available. Includes some plant-drug monographs online.
Martindale's Health Science Guide Extensive worldwide links.