Adding the RPMforge repositories is one of the first things I like to do on a new install. Instructions are on the RPMforge website but it is as straightforward as:
rpm -Uhv rpmforge*
You will then notice the repo details in /etc/yum.repos.d
This allowed me to update Spam Assassin from the 3.1.9 version in the CentOS/Red Hat repositories to version 3.2.4.