Classic texts: Hool 1922.
Classic texts: Scudder's Materia Medica, 1898: Alteratives.
Classic texts: Eli Jones' Definite Medication, 1911.
Classic texts: Ellingwood 1910.
Henriette's herbal is one of the oldest and largest herbal medicine sites on the net. It's been online since 1995, and is run by Henriette Kress, a herbalist in Helsinki, Finland.