MedicineNet provides a comprehensive, alphabetical listing of medical conditions, diseases and treatments. The database, which is posted on MedicineNet.com, is easy to use and provides medical listings in simple, non-medical language.
Reference.MD also has an alphabetical list of diseases based upon the type of condition. For example, the heading of "Skin Diseases, Infectious" contains listings for cellulitis, dermatomycoses and other diseases that fall into that category.
Articles on MedicineNet.com and Reference.MD are peer-reviewed, with many entries coming directly from the National Library of Medicine, the National Institutes of Health Unified Medical Language System, and from board-certified physicians. PubMed is run by the National Institutes of Health and provides access to entries from many published medical journals, and is a good site to find more in-depth information about diseases and conditions.