The Guide to Aromatherapy
An extremely useful page with notes on dozens of oils and how to use them. Huge links section.

Aromatherapy and Healing
A site that offers suggested treatments for specific ailments.

Scentsible Aromatherapy
A very useful page with a list of specific oils, their properties, uses, and precautions. Also a good collection of articles on aromatherapy.

Aromatherapy page at the homepage for Frontier Herbs and Aura Cacia. Shop around before buying oils here, but the page has a lot of useful information. An extensive list of oils, online copies of two newsletters, and advice to help you get started.

Aroma Vitae
A small page with little detail but some essential information presented in a succinct and straightforward way. Might be a good starting point.

Aromatherapy, A Scented History
A well-written article on the history of aromatherapy.

an article on Aromatherapy in Migraine treatment on the Canberra Migraine Support Group pages. Good information on general techniques for using oils.

The Aromatherapy Resource Group
Basically a resource page for two distributing companies and a correspondence course, they do have a useful links section (but I've put most of the ones that are still active in this list!)