The Javanomicon (2004)
The Javanomicon is a fully-featured electronic textbook that will help you develop your Java skills in new and interesting directions. The whole focus of the book is on a sense of progress - after each chapter, you should be able to do something new that you weren't able to do before. The book is Fundamentals First and concentrates on understanding rather than the 'correct' way to do things. The book is currently in its Delta draft, but was extensively updated from Java 1.4 to Java 1.5 - as such, there may be inconsistencies in the text. Let me know if that's the case!
The Javanomicon is a Level 2, Intermediate textbook. You are expected to be proficient with all introductory Java (or another c-type) programming syntax. Those readers who are not familiar with these should instead begin with the Javanomicon programming book.