I am surprised to see that no one has mentioned ClearOS (http://www.clearfoundation.com/). While there is a charge for support, the software is free of charge. I believe that it is based on RH as well meaning that if you have a grasp on RH and the supporting software installed you could forego the cost of support packages. It's not perfect, but it does provide an easy to use web gui for administering nearly every aspect of the system. It can also be implemented as nearly transparent to end users.