we're an ISV about to deploy our SaaS application over the internet to our end users, and are currently looking for an application monitoring solution. In addition to monitoring the usual OS-level suspects (I/O, disk space, logs, CPU, RAM, swapping, etc.), we're also looking to monitor, alert and report on internal application events, conditions, and counters (think queue size for internal service, or latency of a service we're getting from a third party via custom APIs).

We're started looking at Nagios, Zenoss, etc., but found out those do only low-level stuff, and are currently looking at MOM and ManageEngine. Still, they are far from being an custom app monitoring tool.

So - do you have anything to suggest?