[Linux-cluster] Cluster/Server Monitoring tool

[isplist at logicore.net]

Is there something that most folks here would agree on as an open source 
monitoring solution for my cluster?

I am finding it very difficult to figure out where I am having problems with 
my cluster. I have a test setup using three web servers behind an LVS server. 
There are two other machines connected but they are for maintenance, not 
application serving. 

When users connect to the site from remote, there are huge long delays between 
page changes. Sometimes, having to click reload/refresh over and over again. I 
need to figure out what's going on, loads, cpu usage, memory, basic things. 
web server stats for load and such would probably help too.

Thanks in advance.

Mike