Benedetti and Cranley's Head First jQuery
The e-book, distributed only in PDF due to the highly visual content, may be a bit hard to use on some e-readers (in special, the e-paper based ones like the Kindles and Nooks).
It's also a book for beginners. It will cover the basics and put you on track to understand and build upon more complex stuff, but won't take you there. It offers easy reading and the very visual and conversational style, albeit annoying at times, seems to be very effective in increasing memory retention. As with any programming book, this one is better read with a computer on the side.
In short: if you are new to jQuery and want to quickly get a grasp of it, this book will be helpful. If you are already somewhat familiar with jQuery, this may not be the right book for you.