Hi, I'm really into the open source software. I'd use nagios in your localhost, with a friendly interface as to allow you to administrate and make changes. I can also recommend Zenoss, which is also very friendly. I work as a Linux administrator, in charge of the monitoring systems, right now I'm monitoring a farm of 500+ servers, most are Linux and Windows, with some Solaris, including Mysql, MSsql and Oracle databases.