I bought a copy of the 'Ashley Book of Knots', for my birthday, from Amazon.com. Some consider it the knot tyer's bible. One of my sisters gave me a gift certificate, so that brought the book into a more affordable range for me.
The book is huge at 640 pages, 3900 different knots, and 7000 illustrations, although a lot of duplicates in some of those knots, as I've been told by other knot tying friends that are more familiar with the book. It simply reminds me that I'm still just an amateur at knot work and there's always more to learn for those that want to. :)