- Learning GNU Emacs, 2nd Edition by Debra Cameron, Bill Rosenblatt, Eric S. Raymond
Much better than the current, 3rd edition. The first half of the book walks you through the fundamental steps, as a tutorial.
Can be obtained from O'Reilly http://shop.oreilly.com/product/9781565921528.do
- Casting Spells in Lisp (Emacs Lisp version) by Conrad Barski M.D.
Written originally to teach some other flavor of Lisp, the book has been modified for Emacs Lisp. The presentation is in a form between a comic book and a manual that educates while you have fun. The best of both worlds.
It can be read online here.
- Xah Emacs Lisp Tutorial - This concise and concrete tutorial focus on practical needs with examples.
There are many Twitter accounts dedicated to sharing news and tips about Emacs. One can benefit a lot by following them:
Before you install a lot of extensions, explore your Emacs distribution! Try(M-x find-emacs-packages) to browse the available packages by category.