I use Fiveruns for rails app monitoring, which doesn't seem to be on your list. That gives me an idea of how fast my app is running, where the bottlenecks are etc.
Then I have monit setup to keep an eye on server load, hd's, nginx, postfix + dovecot etc, and if monit fails to restart services for whatever reason, I have pingdom as my last line of defence, at which point I look into it manually.
Then I have monit setup to keep an eye on server load, hd's, nginx, postfix + dovecot etc, and if monit fails to restart services for whatever reason, I have pingdom as my last line of defence, at which point I look into it manually.