Ellen Finkelstein writes a little book called the AutoCAD Bible and AutoCAD LT 2012 Bible.
She also has a AutoCAD Tips Blog, writes on using Power Point effectively, gives presentation training and consulting along with speaking. When she is not doing anything else she chairs Over-Achievers Anonymous when most people giving into sleep.
All that aside, my favorite resource for everything AutoCAD has been and continues to be the AutoCAD Bible. When I say that, I think that the facts back me up. Case in point....
A few years ago I had the pleasure of meeting with Ellen, Lynn Allen and other Bloggers at an AutoCAD launch event. When we all introduced ourselves, Ellen said "My name is Ellen Finkelstein and I write the AutoCAD Bible." Lynn introduced herself this way. "Hi, my name is Lynn Allen. I have written 5 books on AutoCAD, and if you stacked them all up, they wouldn't be as thick as Ellen's!"
Go to Amazon right now and buy a copy for yourself, and one for a friend.