We have a few book recommendations at https://wordpress.org/about/books/
With that said, WordPress shoots for major updates 3 times a year (the next one is on target for April 2016), so anything in print will be outdated soon (if not already).
For using WordPress, we recommend https://codex.wordpress.org/Main_Page (there’s a new thing in the works for this)
For developing with WordPress, we recommend https://developer.wordpress.org/
I was thinking buy this one: Professional WordPress: Design and Development 2nd Edition. I am read the codex and developer web site. But for a newbie it would be better read a book, because sometimes I feel lost on the web site…
Looks like there’s a third edition out now, published 2015, so I recommend that over the second. 🙂
I found “Digging into WordPress” really good – very easy to follow for a relative beginner. https://digwp.com/book/
