RedHat/CentOS 5:

32Bit:

wget http://pkgs.repoforge.org/rpmforge-release/rpmforge-release-0.5.3-1.el5.rf.i386.rpm
rpm -ivh rpmforge-release-0.5.3-1.el5.rf.i386.rpm

64Bit:

wget http://pkgs.repoforge.org/rpmforge-release/rpmforge-release-0.5.3-1.el5.rf.x86_64.rpm
rpm -ivh rpmforge-release-0.5.3-1.el5.rf.x86_64.rpm

RedHat/CentOS 6:

32Bit:

wget http://pkgs.repoforge.org/rpmforge-release/rpmforge-release-0.5.3-1.el6.rf.i686.rpm
rpm -ivh rpmforge-release-0.5.3-1.el6.rf.i686.rpm

64Bit:

wget http://pkgs.repoforge.org/rpmforge-release/rpmforge-release-0.5.3-1.el6.rf.x86_64.rpm
rpm -ivh rpmforge-release-0.5.3-1.el6.rf.x86_64.rpm

RedHat/CentOS 7:

wget http://pkgs.repoforge.org/rpmforge-release/rpmforge-release-0.5.3-1.el7.rf.x86_64.rpm
rpm -ivh rpmforge-release-0.5.3-1.el7.rf.x86_64.rpm