I have just finished reading Matt Butcher’s latest book, Drupal 6 JavaScript and jQuery, published by Packt Publishing - ISBN 978-1-847196-16-3. It is a good read. It is one of those books that arrived at the right time and left me inspired.
I have always leaned towards Yahoo’s YUI toolkit when I need an Ajax framework, while the rest of the time I just bash out a bit of JS to get the job done.