What is the best software for network performance monitoring?

What software is considered the best for total network performance monitoring. I am in search of a software that will monitor our switches, routers, firewalls, and the overall performance of our network. This is a network running Win 03 as the OS, and has around 60-80 servers. Any suggestions? What are the pros and cons of such software?

Lots of commercial products will do this. But they tend to be expensive to buy and expensive to scale because of licensing.

Look into an open source solution. Try the link below: