Mrs Grieve's Modern Herbal Online Version of this standard reference work

Thomas Schoepke
Plant Image Gallery

A collection of photographs and old prints of plants and herbs
Botanical Dermatology Database A searchable database of plants and their dermatological effects

Tree of Life

An excellent guide to taxonomy though only parts are done
Integrated Taxonomic Information System An authorative taxonomic website
The Interesting site on trees with stories and folklore