there are all the good books on this website. Check them out.
William Cheung is really good and is one of the best WC masters that I have seen. And I have heard that his books are enlightening, I intend to by a couple.
James Yimm Lee has written the first book in that list and is a really good book containing sil lum tao and some trapping techniques. That was the first book that I read and helped me a lot on my positioning, a very important aspect of WC IMO.
and the book by joseph which is not listed is:
Wing Chun Kung-Fu: Basic Forms & Principles
and the other two books that he has written are listed there. grappling &fighting, advanced weapons and techniques.
The last book contains the pole form and the WC butterfly sword form