If I had just one book to buy it wouls be this one
http://www.chapters.indigo.ca/books/item/books-978074321241/074321241X/Pregnancy+Childbirth+And+The+Newborn+Revised+And+Updated+The?ref=Search+Books%3a+'childbirth'
it is a very very good book, particularily about birth, it explains all the options out there, with no bias one way or the other, just the facts. I really didn't like the what to expect series myself. It didn';t really tell me anything I didn't already know. I bough A LOT of books and this one was the best by far. The rest were okay to read, but not useful knowlegde wise.