I approached Ajax Design Patterns, by Michael Mahemoff, with some trepidation. I am suspicious of design patterns, because like many useful ideas, design patterns are often overused, followed dogmatically, or used as a substitute for understanding.
The book packs an enormous amount of information. It is probably heavy for a beginner, but ADP does a great job of starting at the beginning and moving all the way to advanced topics. There are tons of references throughout, so ADP functions not just as a book but as a roadmap.
Finally, there is one particular detail that I loved about this book. Rather than bury me under sample code, the samples include just enough code to make the point. The complete sample code is online, so this tradeoff is perfect for me. If you are looking to work through the code in the book yourself, you will have to fill in the blanks or get the code online.