No mention of Wackamole¹ in the article, and I feel really compelled to mention it here, as it is really simple to set up a HA cluster using it. I followed this howto² a few months ago. It was really easy to configure and it runs stable since.

¹http://www.backhand.org/wackamole/

²http://www.howtoforge.com/setting-up-a-high-availability-loa...