If you run PHP on your webserver, you can make it more secure by installing Suhosin. To quote from the Suhosin website:
Suhosin is an advanced protection system for PHP installations. It was designed to protect servers and users from known and unknown flaws in PHP applications and the PHP core.
If you’re running Debian Etch, all you need to do is run
apt-get install php5-suhosin
and you’re all set.
I’m going to give this a go, reinstalling my server, going to hop from FreeBSD after about 4 years back to Debian. Also, to better secure Apache, and PHP for that matter, install mod_security and rules from gotroot: http://www.gotroot.com/