Rating: 

I recommend reading "Ajax The definitive guide"
if you have loads of time and if you are new to AJAX techniques. It would also be a great book to use as a reference book.

The book gives loads of information and clear examples. The book features a clear structure wherein every single part of using AJAX gets his place.

Those "loads of information" also make it a bit difficult to read , sometimes you have to read parts again to fully understand it.
^{I have to remark that English is not my native language. A Dutch review will appear shortly here (http://www.compublog.nl) .}