[zimbatm]

Widening the net a bit but since you added network-connected monitoring, check out sensu. It's backward-compatible with nagios plugins and handles cloud systems very well (no need to restart the server every time a host is being added/removed). It's also capable of extracting system metrics and forward them to graphite/... . Really great tool.

And just for metrics, collectd is great too.

[adionditsak]

Nice zimbatm, i will definitely take a look at those :-) Sounds great with Nagios + cloud systems integration.

[samstave]

While I agree that Sensu could be cool, their utterly uninformative website makes me want to break the fingers of whomever was in charge of that site design.

Worst website design EVER for any monitoring system in existence.