Eric Burke: If you are learning Hibernate, you *must* buy Hibernate in Action, by Christian Bauer and Gavin King. I skipped around a lot but now I'm trying to read it straight through. It is an essential tutorial and reference. A lot of the book examples are very similar to what's in the HTML docs that ship with Hibernate, but the book is more polished and easier to read through. The book really helped clarify the architecture of my application.
I completely agree with Eric here. I'm reading the book cover to cover and it's a fascinating read. Even if you are not using Hibernate, reading this book will give you hints on how to design your persistence layer, and your application architecture will be more clear.
I also happens to like the expository style of the authors---very engaging and lucid. There is an effortlessness in the text that could only result from tremendous technical insight and literary discipline. They (Christopher Bauer and Gavin King) make it look easy.
Plus, I love the little "cliffhangers" at the end of a section that lead you into the next section. It reminds me of the classical Chinese novels where chapters usually ends with something like "The door swung open. In comes a big man. To learn who he is, read the next chapter!"