Great and free book series YDKJS. I am reading these series now and they are great and easy to understand. Good luck.
It’s written by John Resig, the original author of jQuery who now works for Khan Academy in their computer science area.
I find the book extremely valuable and filled with a lot of great, real world data. It deals with a lot of relevant issues, and looks at how features in various JS libraries were implemented - not just jQuery (in fact, he mentions jQuery very little compared to other libraries such as prototype).
It’s not a beginners book, but has a lot of great data.
For straight jQuery, jQuery: Novice to Ninja was a great one …