Nagios - measuring that the application and database is up, and that disk and load are ok. (also ping but that is redundant). I use exception notifier for rail

Nagios - measuring that the application and database is up, and that disk and load are ok. (also ping but that is redundant). I use exception notifier for rails. Simple, but it works. Might switch to newrelic. From time to time I also use pingdom.com to see that the site is available from different networks around the globe.