One Book...

If you could only offer a single book (or source, so URL's but not one with a million links or essays) in which to suggest to someone curious about learning (and potentially) joining your religion, what would it be?

Remeber, ONE (SINGLE) book suggstion. Also feel free to explain what it is this book offers over others.

I'll go first. I mean in terms of specifically CR books, I can count them on one hand (Using only one finger )

So it would deffinetly be the Celtic Reconstructionist FAQ book (Which is the CRFAQ website, in pulped dead tree format).
It covers the basics of everything anyone would need to know about CR to develop an accurate image of the tradition, and has a huge book list from which to further develop ones knowledge. It is essential reading for anyone who either want to know more or become a CR.

Since I dont have a religion so to speak I can still pick "The story of B" by Daniel Quinn

The Upanishads.

Maya

Black Elk's: The sacred pipe.

The first Zen sermon was delivered by the Buddha and he didn't use any words, not even one word, he simply held a lotus over his head for all the world to see... And I'm supposed to choose a book full of words?

Although it's not a Zen book, I'll contend that it is the foundation and corner-stone of Zen, I choose; The Tao Te Ching.

"The Tao that can be spoken
is not the eternal Tao."

- Tao Te Ching

The Poetic Edda

Lee M Hollander translation. The arrangement of the poems allows for you to learn the kennings and references that are used in the later ones. Although it is a translation, it has kept the poetic form through idiomatic translation rather than literal.

Lessons In Truth by H. Emilie Cady.