[ddbb]

Using OSSEC (open source).

Seriously, it puts rkhunter, logcheck and all these old tools in their toes..

Check http://www.ossec.net

It monitors your logs, file changes, etc all by default, simple to install, etc.. I love it.

[sucuri2]

+1 for OSSEC. It is my preferred one for sure. I use that to monitor my Apache logs, Wordpress, SSH and a few more.