What files to backup

[Gary Roach <gary719_list1@verizon.net>]

I have three  standard Debian Squeeze systems and am setting up Backuppc 
to backup to an extra hard drive I have on one of the systems. I plan on 
backing up the following directories:
    /etc
    /home
    /var/www (An Apache server resides on one of the systems)
Is there anything else that should be included.

Gary R.