What tool do you use to monitor your servers?
I am currious to know from the community which monitoring applications are the best and simplest to install and use for the Linux platform. Please keep in mind that we need the ability to monitor multiple servers and install the monitoring easily with little maintenance.
Open source would be ideal but I am also currious into alternative low cost options.
Personally I like the idea of splunk but I guess their open source version is very limited.