CVS On-Line Pharmacy Store A true on-line pharmacy providing wholesale pricing information; this particular page lists their top-selling several hundred products.  Very informative, especially for comparing the retail price of a drug you or a friend may take with the wholesaleprice.

DrugDigest - "DrugDigest is a noncommercial, evidence-based, consumer health and drug information site dedicated to empowering consumers to make informed choices about drugs and treatment options.

Drug Information (PDRhealth) - the site installed by the publishers of the PDR, now that it is no longer available unless you are a drug prescriber. Its resemblance to the PDR is similar to the similarity of watered-down root beer to the real thing...... 

Drug Interaction Checker from a very good interactive utility for checking whether two or more medications you've been prescribed have the potential to interact with each other in a harmful way. - Welcome to the most popular, comprehensive and up-to-date drug information resource online. Fast, easy searching of over 24,000 approved medications. Possibly the most complete, comprehensive, authoritative site on all aspects of drug therapy on the entire web. 

Drugs & Medications A-Z part of the great WebMD site, this huge resource enables searching on either the drug name or the condition for which it was prescribed; there's also an excellent pill identifier page.

Medications - Internet Mental Health- a large amount of information on most pharmaceuticals used in the treatment of mental illness.  Similar to Rxlist (below), but confined to this single drug area. Thus, the information available is somewhat more extensive on each drug contained.

MedicineNet -a huge amount of health/drug data written by physicians, covering every imaginable topic. 

MedLine Plus contains consumer information on over 9,000 Rx and OTC medications.  Very nicely done, but there is no real technical data, such as mechanisms of action, metabolism, pharmacokinetics, etc.

The National Library of Medicine's MEDLINEplus Not only MedLine, but also many links to medical dictionaries, libraries, databases, publications and news.   Very worthwhile.

Physicians' Desk Reference (PDR) - no longer available on-line, unless you're a physician, nurse, or other potential drug prescriber.

RxList The best overall collection of specific data on all prescription drugs, very similar to that contained in prescription inserts.  Includes chemical data, contraindications, interactions, pharmacokinetics, metabolism, how supplied, instructions to patients, etc. Also features a pill identifier section, a part on supplements, many great slideshows, even a "symptom checker"! Check it out! 

U.S. Pharmacopeia   establishes purity standards for thousands of drugs for human/verterinary use.