The following links leads to web pages that I believe contain quality information on herbal medicine.
The South West School Of Botanical Medicine Home Page: This site created by herbalist Michael Moore has thousands of pictures of medicinal plants as well as information on specific herbs, medical publications from the 1800's (when doctors were still using primarily herbal medicine), and the teaching material for the school.
Howie's Herbal Web Site: The home page of a teacher and wildcrafter in Oregon. Howie's (aka Mr. ATP) site contains much information about herbal medicine with an emphasis on the conservation of wild medicinal plants.
The California School of Traditional Hispanic Medicine: This is the home page of Chuck Garcia, a Curendero as well as a teacher of his craft. Class schedules are updated on a regular basis.
Medscape: Search 'medline' (the national library of medicine database) and other medical information databases for free. This site also has a whole host of information from the medical world ranging from drug information to medical news. Membership is required for access to the site, but it is free.
Robyn's Recommended Reading: This page has several links related to literature that is available on the topic of herbal medicine and related subjects.
Henriette's Herbal Home Page: A very informative sight managed by the eminent Finnish herbalist that covers a broad range of herbal interests.
Medicinal Herb FAQ: A compilation of postings from the alt.folklore.herbs news group maintained by Henriette Kress. Includes info on some of the most purchased herbs.
The Pacific School Of Herbal Medicine: This school is run by bay area herbalist Adam Seller. Classes at this school are perfect for those wanting to take classes that are both in depth and full of practical knowledge. Adam has been one of my teachers, and I consider him to be the one who taught me the bulk of what I needed to become a practitioner of western herbal medicine.