The best thing I could recommend for Druid info is a book called The 21 Lessons of Merlin.. its part story, part information. The information pages at the end of each chapter supplement and clarify the story itself. It's a great read, and gives the best examples I have seen so far for Druidry. It is a story, so you can't just jump in anywhere. And remember sometimes you must read between the lines to get past the "static", as well as the curse of language( poor translations/examples). Be blessed.
Finding good books on Druidry and Celtic studies is very difficult in most US bookstores. If you enter the local Waldenbooks or Barnes & Noble you will likely find mainly books from Llewellyn publications. You can always recognize these books by the crescent moon emblem on the bindings. Most of these books are not well researched and are more for fun than serious study. There are exceptions, however, including the two bookslisted here by Steve Blamires. Most of the better books on the Druids and modern Druidry are written today by British authors whose works are often hard to find in these stores. Fortunately, with the advent of the Internet, you can order any book in print from such online bookstores like Amazon.com. Here's a list of some of the better books on Druidry a Now on with the good books!
Berresford Ellis, Peter "The Druids ",
Blamires, Steve "Glamoury: Magic of the Celtic Green World ",
Blamires, Steve "Celtic Tree Mysteries, Secrets of the Ogham ",
Carr-Gomm, Philip & Stephanie "Druid Animal Oracle ",
Carr-Gomm, Philip " Elements of the Druid Tradition ",
Carr-Gomm, Philip "The Druid Way ",
Carr-Gomm, Philip (editor) "The Druid Renaissance ",
Evert Hopman, Ellen "A Druids Herbal for the Sacred Earth Year ",
Matthews, Caitlin "Celtic Book of the Dead ",
Matthews, Caitlin "Elements of the Celtic Tradition ",
Information about the Druids remained very small. They were not records, documents have left. All we can do today is evidence of other people (mostly Romans and Greeks), who were contemporaries of the Druids, and the more recent documents prepared by Christian monks. You will be hard to gather reliable information about ancient Celtic priests, their worldview, philosophy, religion, rites and rituals.
"Because it's Irish" is a pretty terrible reason to join a religion. That'd be like becoming Catholic because you find Latin charming.
You should also be aware that Druidry as practiced today is somewhat reconstructionist, and isn't exactly what the Druids of old practiced. This doesn't mean you shouldn't practice it - Druidry is awesome. It's just not ancient.