I have written a detailed description about the steps to be taken to setup a Debian based server (Debian Sarge alias Debian 3.1) that offers all services needed by ISPs and hosters (web server (SSL-capable), mail server (with SMTP-AUTH and TLS!), DNS server, FTP server, MySQL server, POP3/POP3s/IMAP/IMAPs, Quota, Firewall, etc.).
To make it even better, perhaps you want to include a gld-setup in postfix, to prevent spam and email-viruses. There is a ready to install gld package that you can install with apt-get, and then manually hook up into main.cf. I have found that this kills over 95% of all spam, with a very low false positive rate. Combined with spamassassin its been weeks since i got a single spam, down from about 30 a day...No false positives as far as i know.
Also install ide-smart and set up a cron job to automatically send mail to somebody if a disk is about to fail. Its not 100%, but its better than nothing there.
The list can go on and on as far as i'm concerned, so include what you think is worth while . Good job!