I have added the Debian Handbook to my Resources navigation menu.
The handbook is available at: https://techish.net/debian-handbook/
You can install it on your Debian system (available in Unstable):
apt-get install debian-handbook
The documentation is stored in: /usr/share/doc/debian-handbook/.
You can also download the handbook from Raphael’s site: http://raphaelhertzog.com/2012/05/10/the-debian-administrators-handbook-is-available/ as well as from the handbook development site: http://debian-handbook.info/