I’ve been using jQuery since at least mid 2008 and have to say that I just love how much easier things are and not having to generally deal with the cross-browser issues in Internet Explorer, Safari,Chrome, and Firefox.
In the roughly two years that I have worked with jQuery, I have referred to a couple of things to learn jQuery and improve my web based applications.
Rebecca Murphy wrote an excellent electronic book called jQuery Fundamentals that she gives away for free from her website. jQuery itself also has many video tutorials, and a fairly well written and maintained web based manual that works similar to a Wiki.
Hope this helps!