There are definitely an abundance of books on Eclipse to choose from. One of the latest additions to the field, Professional Eclipse 3 for Java Developers by Berthold Daum (Wrox) is a nice new choice...
Chapter List: Introduction to Eclipse; Effective Programming with Eclipse; The Art of (Visual) Composition; Organizing Your Code; Project One: Duke Speaks; Project Development; Advanced Topics of Project Development; The SWT Library; JFace; Project Two: Jukebox; Developing Plug-ins for the Eclipse Platform; Developing Your Own Eclipse-Based Products; Project Three: A Spell Checker as an Eclipse Plug-in; The Rich Client Platform; Project Four: The Hex Game as a Rich Client Application; Conclusions and Outlook; Useful Plug-ins for Eclipse; Migrating Projects to a New Eclipse Version; Important Downloads; Bibliography; Index
There are a number of things I liked about this book. For one, it deals with the latest Eclipse release (version 3). Although it's not a major problem to mentally translate text between 2.1 and 3.0, it's still easier to learn if both the book and the student are on the same page. Next, Daum concentrates a lot on practicality. The four projects included in the book cover four of the major types of development you'd face as a Java developer. By using the projects during your learning, you should have a good grasp of Eclipse when you're finished. Finally, I appreciate the coverage of the Rich Client Platform. My personal opinion is that this feature of Eclipse is going to be a very big deal, and this book is one of the few that covers it in any detail.
So, if anyone were to ask me for a recommendation on a book for Eclipse, this book would be among the top of the list. It's good stuff.