jQuery Fundamentals is a free online book (there are PDF and ePub versions too) that can be a guide for any developer but specially for JS and jQuery beginners.
It starts from JavaScript basics, moves to jQuery basics and, if you want, there is a detailed chapter on advanced jQuery usage.
All with examples, exercises and their solutions (comes with the download).
Simply, a must-bookmark for every web designer and developer.
Website: http://jqfundamentals.com/book/book.html
Download: http://github.com/rmurphey/jqfundamentals