Ganglia is a very good monitoring tool. You can install backand to tracking machines (sys-cluster/ganglia) and use web frontend (sys-clusted/ganglia-web) to see pretty graphics. After installing backend, you must configure /etc/ganglia/gmond.conf

...
cluster {
  name = "jassy"
  owner = "hoxnox"
  latlong = "unspecified"
  url = "unspecified"
}
...
host {
  location = "jassy"
}
...
udp_send_channel {
  host …