EPEL is a community-driven, Redhat-backed repository for use with Enterprise Linux (and therefore CentOS, Rocks, etc). It provides many useful packages not provided by the official repositories while maintaining compatibility with upstream releases.

See more: https://fedoraproject.org/wiki/EPEL

Install the EPEL RPM directly from the repository. This will add the appropriate .repo file in /etc/yum.repos.d/ as well as the private key needed to verify package integrity.

$ rpm -i http://download.fedora.redhat.com/pub/epel/5/i386/epel-release-5-3.noarch.rpm