Came across this today while looking into fail to ban. This is a pretty good overview of applications you can use to secure your server. The directions are for ubuntu, but source packages and alts are just a google away of course.

Quick ‘n Dirty Security and Visibility

1. Introduction
2. Firewall
2.1 FireHOL
2.2 ufw
3. Intrusion Prevention
3.1 Fail2Ban
3.2 sshdfilter
4. Intrusion Detection
4.1 chkrootkit
4.2 rkhunter
5. Log Monitoring
5.1 LogWatch and Dropbear
6. Security Update Notification

Introduction

This article describes some of the tools and utilities I use to better secure and monitor my servers. Simply following the article below does not get you a secure box, you also need to ensure any services you have running are correctly configured and you should disable, or better yet remove, any services or software you do not require.

Quickn Dirty Security and Visibility