Many of us got started on our path by happening across a book. My book was The Spiral Dance, but the original, not this 20th anniversary edition. I was 12 or 13 and I read The Mists of Avalon, and The Spiral Dance was listed in the concordance as a reference. Miracle of miracles, the local library had the book. It was hardback and had a red cover. I read it over and over. I photocopied long sections because I was so young and yet old enough to know that I would never be allowed to buy the book, at least for a very long time, until I became an adult. Now I do have a copy, but not the original.
My other favorite pagan book is Celtic Magic. As I mentioned in this post, it is a great book for people new to The Craft. You can find history, mythology, goddesses and gods, and ingredients for all types of spellwork in this little book.
Please feel free to add your favorite books to this discussion with a comment.