It's a bit of a pain that many basic third party tools that aren't put of the main Centos/RHEL repositories are not available unless you compile them or install the RPMForge Repo.

*Updated 08/29 with new download location changed from apt.sw.be to rpmforge.sw.be

Here's a quick, simple/cut&paste way to do it:

wget http://rpmforge.sw.be/redhat/el5/en/i386/rpmforge/RPMS/rpmforge-release-0.5.1-1.el5.rf.i386.rpm

rpm -i rpmforge-release-0.5.1-1.el5.rf.i386.rpm

After this you'll be able to install other useful tools such as bmon, etc... things that are available with any Debian based distribution in standard form.