Have you seen:

Learning GNU Emacs: http://www.amazon.com/Learning-GNU-Emacs-Third-Edition/dp/0596006489 <http://www.amazon.com/Learning-GNU-Emacs-Third-Edition/dp/0596006489>
or
Writing GNU Emacs Extensions:  http://www.amazon.com/Writing-GNU-Emacs-Extensions-Glickstein/dp/1565922611 <http://www.amazon.com/Writing-GNU-Emacs-Extensions-Glickstein/dp/1565922611>
or
An Introduction to Programming in Emacs Lisp: http://www.amazon.com/An-Introduction-Programming-Emacs-Lisp/dp/1882114027/ <http://www.amazon.com/An-Introduction-Programming-Emacs-Lisp/dp/1882114027/>

I’ve read the first two, albeit long ago. I don’t think that they were unpopular, but also I don’t think that they were especially popular.

~Chad