One book that I have mentioned before but I think it deserves to be in here is On Single Combat by K.Kernspecht it is based on Wing Tsun and explains everything in good detail.
I would also have to add Blitz Defence by K.Kernspecht to be a great book.
I recommend both of these as a must if you are studying Wing Tsun or are just interested.
Happy Reading
Train Hard Tez WT Central