Shocked at the lack of zabbix. Alerts, graphs, history, all in one place. Install the agent and you get the basics for free - I just set up a demo of it a couple days ago in 30 minutes flat.
Me too. This is what I use. It was dead simple to setup. It had great default settings. Pfsense also has an agent package available for it and is a one click setup. It was also very easy to setup custom scripts for monitoring my custom back end software. I tried nagios, hobbit, opennms, and others recently and zabbix worked best for me.
I've been using zabbix for around 4 years now for all my monitoring needs, and i love it. In fact, I love it so much, that I decided to launch a hosted 'zabbix as a service' company this year, check it out: http://tribily.com