Server monitoring solution?

I would like to know of a good server monitoring solution. I was using Spotlight on Windows by Quest Software. I love the GUI they developed. It shows a real time graphical representation of my server(s) performance. Unfortunately Spotlight on Windows does not support Windows Server 2008 properly and I have had to stop using it. I would like to know what many of you are using as a server monitoring solution. I have attempted to setup Nagios on Ubuntu, but with little success. I look forward to your responses. Thank you in advance for your help.