RHEL and Fedora Yum Repository

Run "yum install yum-fastestmirror" and "yum install yum-priorities" to install these two yum plugin. Refer http://wiki.centos.org/AdditionalResources/Repositories/RPMForge?action=show&redirect=Repositories%2FRPMForge.

RHEL or CentOS (i.g. 5.x)Yum Repository:
EPEL : http://fedoraproject.org/wiki/EPEL. Follow http://fedoraproject.org/wiki/EPEL/FAQ#howtouse
su -c 'rpm -Uvh http://mirrors.sohu.com/fedora-epel/5Server/i386/epel-release-5-4.noarch.rpm'

CentOS :

rpmfusion : http://rpmfusion.org. Follow http://rpmfusion.org/Configuration
su -c 'rpm -Uvh http://download1.rpmfusion.org/free/el/updates/testing/5/i386/rpmfusion-free-release-5-0.1.noarch.rpm http://download1.rpmfusion.org/nonfree/el/updates/testing/5/i386/rpmfusion-nonfree-release-5-0.1.noarch.rpm'

atrpm : http://atrpms.net. Follow and do as http://atrpms.net/documentation/install/
rpm --import http://packages.atrpms.net/RPM-GPG-KEY.atrpms

RPMforge : Refer https://rpmrepo.org/RPMforge/Using and http://wiki.centos.org/AdditionalResources/Repositories/RPMForge?action=show&redirect=Repositories%2FRPMForge to enable it.

DAG (RPMforge include it now) : http://dag.wieers.com. Follow http://dag.wieers.com/rpm/FAQ.php#B
rpm -Uhv http://apt.sw.be/redhat/el5/en/i386/rpmforge/RPMS/rpmforge-release-0.3.6-1.el5.rf.i386.rpm
or
rpm -Uhv http://apt.sw.be/redhat/el5/en/x86_64/rpmforge/RPMS//rpmforge-release-0.3.6-1.el5.rf.x86_64.rpm

Dries : http://dries.ulyssis.org/rpm/

Fedora (i.g. 13)
rpmfusion : http://rpmfusion.org. Follow http://rpmfusion.org/Configuration
su -c 'yum localinstall --nogpgcheck http://download1.rpmfusion.org/free/fedora/rpmfusion-free-release-stable.noarch.rpm http://download1.rpmfusion.org/nonfree/fedora/rpmfusion-nonfree-release-stable.noarch.rpm'

Reference:
http://rpmfusion.org/FedoraThirdPartyRepos
http://www.mjmwired.net/resources/mjm-fedora-f13.html
http://wiki.centos.org/AdditionalResources/Repositories
http://www.my-guides.net/en/
http://fedorasolved.org/Members/zcat/yum-rpm-faq