Several...Some might be a little advanced for the layperson. Since I work in pharmacy, I am on all the mailing lists for too many sites. There are more, but I am running out of time. How many are we allowed to post?

BehaveNet
Merck
AllPsych
Internet Mental Health
American College of Cardiology
US Food and Drug Administration Medwatch
US Food & Drug Administration CDER - Center for Drug Evaluation & Research
MicroMedex
MerckMedicus
Medscape
Epocrates Online