Sorry for the numerous posts. I keep thinking of more things to add.
OBOD is pretty expensive, but from what I've researched, they mail you alot of good information in either audio format, text format, or both.
New Order of Druids is free if you take on their course without a mentor. They sell a book for each grade with is about $15.
AODA requires (if I remember correctly) a $50 membership fee, and then $100 for each degree you pass through (apprentice, companion, adept). They also list their entire curriculum for each degree on their website.
Personally I'm tossed up between which three I think would be a better option. If anyone has an opinion on the three, I'd love to hear it.