Seconded. I used Rocks to build clusters for the university for which I worked, and it made my life much, much easier.
If you are already familiar with Redhat administration, you'll be happy to know Rocks can use either Redhat or CentOS as its base OS.
It uses meta-packages called "rolls", which completely automate the installation and configuration of your computing nodes. There are rolls that include most of the commonly used commercial and Open Source HPC software out there, or you can "roll" your own. Basically you just configure your head node, and then adding a compute node is as simple as setting the BIOS to boot over PXE, plug it in, and done.
Rocks, well, rocks.