Depending on your organization’s size, there are a few good tools.
Solarwinds Orion, HP Openview, MRTG, CiscoWorks are all good tools depending on how big your organization is and how much you want to spend or how much you need to see / do.
If you want something for security, you’re a Cisco shop, and are using IPS / IDS etc. a good product is Cisco MARS.
I’m surprised this question sat unanswered for so long.