Since i'm employed by Netmon (netmon.ca), I tend to drink my own kool-aid and use it most. That being said, since most of the products mentioned above are free,

Since i'm employed by Netmon (netmon.ca), I tend to drink my own kool-aid and use it most. That being said, since most of the products mentioned above are free, i'm assuming price is a big concern, so I would recommend looking for the simplest product to meet your needs. There really aren't any standards in this industry in terms of how to present monitoring data to users in a predictable way, and some solutions are abysmally complex, while others are simple but barely show you any important data. I kind of like the nagios/zenoss relationship model, where nagios provides a great open-source platform for monitoring and analysis, and zenoss provides a clear emphasis on simplicity, presentation and automation on top of that platform. I think you should check those out, and i'm interested to see how that relationship and that business model develops in the future as well. If you do have a budget for your monitoring solution though, there are some pretty cool solutions out there, but i'm obviously biased, so i'll refrain from going on a long diatribe about it.