Of the various monitoring tools I used, I found HP Sitescope meeting all the needs of infrastructure monitoring. The best feature about Sitescope is that it allows agentless monitoring. You need not bother about installing any agents on your devices. Further it supports lot of technologies and Operating Systems.
With Sitescope in place you won’t need any other tool for monitoring your infrastructure. Interface of Sitescope is very simple and easy to use. It also provides various tools like performance counters tool, event log tool, trace route tool that help to setup proper monitoring.
Sitescope does not store monitoring data in database, which is another great feature. It provides variable monitoring frequency option. You can increase the granularity upto 15 secs. Most of the infrastructure monitoring tools whether paid or open source, are no match for Sitescope yet. Most of the paid as well as opensource tools rely on SNMP protocol for agentless monitoring. Sitescope supports monitoring via SNMP but it has better agentless monitoring features e.g. for windows it has the ability to monitor via Direct Registry Queries.
There are open source tools like Nagios that use SNMP for agentless monitoring, paid tools like SevOne (Severity One) also use SNMP for agentless monitoring. Monitoring devices via SNMP is not that simple. Sitescope has simplified agentless monitoring further and made it quite easy.