I considered writing an informational post about Artemis for today, but seriously, if you want to know about Artemis? Just go here...
Artemis on Theoi.com - General information, hymns, myths involving her, titles, ancient worship, paintings and statues, and more. I don't think there's a site out there with more information all in one place. Frankly, if you're interested in any of the Greek deities, spirits, etc, Theoi should be your first stop.
Artemis: Virgin Goddess of the Sun and Moon A book similar to the site above, but often going into much more detail. Explains the origins of titles, details of symbolism, mythology, talks about ancient festivals, and so on. It's very nice to have a book with all that in one place. However, in my opinion, the book is a bit expensive for what you get... If you have a kindle, that edition is considerably cheaper.
Now that's a helpful place to start looking at the historical information, but what about her modern worship?
Unbound: A Devotional Anthology for Artemis -This is a fantastic book filled with poems, prayers, essays, short fictional stories, stories of personal experiences with Artemis, all written by different devotees of Artemis.
Dancing in Moonlight: Understanding Artemis through Celebration - A book about the ancient festivals of Artemis (and some modern additions), and how one can celebrate them, either alone or in a group. The author does a good job pulling from historical sources when possible, and is honest when something modern is added.