USP DI volume II Advice for the Patient - see Micromedex above.
Medline Plus Drugs & Supplements - Prescription and over-the-counter medication information from AHFS Consumer Medication Information.
Safemedications.com - Searchable database based on ASHP's AHFS Consumer Medication Information.
MayoClinic.com - Drugs and Supplements
Express Scripts - Consumer health and drug information website of Express Scripts, Inc. (ESI), an independent pharmacy benefit manager (PBM)
British National Formulary (Free registration required)