Making my web server secure

I followed the suse10.1 perfect setup, installed apache, mysql, php and ispconfig.

I was able to build a php page with content from a database so everything is working fine.

So now, before I put the site on the outside, what do I need to look for, install or test out to make my web server secure.

My web server will be behind a hardware firewall.

 

Have a look at tools such as chkrootkit, rkhunter, DenyHosts, portsentry, logcheck, etc.

 

Thanks, I've tried rkhunter and DenyHosts. I think that's all I need for the moment.