Native Remedies Store - http://www.nativeremedies.com/ They have a lot of valuable information besides trying to sell you things. And they include a section for pets.
Chinese Herbs Direct - http://www.chineseherbsdirect.com/ Store. They actually allow you to purchase not only teas and pills, but raw herbs and powders.
The Herbal Remedies reference Guide (probably one of many on the internet) - http://www.all-natural.com/herbguid.html Will tell you what some herbs are used for, how they came about but not necessarily the how of use.