Java Persistence and Hibernate book
English ebook on Hibernate and Java Persistence I used to update for a couple of years. You can read the version for free now. It covers Hibernate 4 and JPA 2.
Extensive, easy-to-follow introduction to Hibernate. It starts from the beginning and
will still be a great help when you deal with performance tuning or Hibernate architecture.
It is full of examples showing you how things look like in real code.