Professional Ajax, 2nd Edition (Programmer to Programmer)
624 pages; Publisher: Wrox; 2 edition (March 12, 2007)
Language: English; ISBN-10: 0470109491; ISBN-13: 978-0470109496

Enterprise AJAX: Strategies for Building High Performance Web Applications
496 pages; Prentice Hall; 1 edition (August 4, 2007)
Language: English; ISBN-10: 0132242060; ISBN-13: 978-0132242066

Writing for enterprise developers, architects, and user interface specialists, the authors explain why AJAX offers such great promise in large-scale development. Next, they systematically introduce today’s key AJAX techniques and components.

Adobe AIR with Ajax: Visual QuickPro Guide by Larry Ullman
Peachpit Press; 1 edition (May 12, 2008); 384 pages
ISBN-10: 0321524616; ISBN-13: 978-0321524614

Adapting to Web Standards: CSS and Ajax for Big Sites (Voices That Matter) by Christopher Schmitt, Kimberly Blessing, Rob Cherny, Meryl K. Evans, Kevin Lawver, Mark Trammell
New Riders Press; 1 edition (December 24, 2007); 288 pages
ISBN-10: 0321501829; ISBN-13: 978-0321501820

Pragmatic Ajax: A Web 2.0 Primer by Justin Gehtland, Ben Galbraith, Dion Almaer
Publisher: Pragmatic Bookshelf; 1 edition (February 1, 2006)
200 pages; Language: English; ISBN: 0976694085; 6.01 mb

It's not just another book on Ajax. It's Pragmatic Ajax: a concise, complete look at a new way of envisioning and implementing browser-based applications.