Extra Packages for Enterprise Linux (EPEL): RHEL4, Centos5

http://fedoraproject.org/wiki/EPEL hosts some useful, extra RPMs for RHEL4 and RHEL5 distros:

mercurial, trac, steel back common lisp, rrdtool, clam av, openvpn, deny hosts, rsnaphot, pound, moin, plone, zope.

Update your yum sources (no apt repository it seems as yet) by installing the epel-release RPM and yum install them.

http://download.fedora.redhat.com/pub/epel/4/i386/repoview/epel-release.html
http://download.fedora.redhat.com/pub/epel/5/i386/repoview/epel-release.html

RPMForge: Third-party repo

The RPMForge guys provide stable, common packages which are missing from the main repositories.  The easiest way to add their repositories to your sources is by installing their latest RPM: http://dag.wieers.com/rpm/packages/rpmforge-release/
( v0.3.6 as of this writing).  e.g.

 rpm -Uhv http://apt.sw.be/redhat/el5/en/i386/rpmforge/RPMS/rpmforge-release-0.3.6-1.el5.rf.i386.rpm 

or for x86_64 machines

rpm -Uhv http://apt.sw.be/redhat/el5/en/x86_64/rpmforge/RPMS//rpmforge-release-0.3.6-1.el5.rf.x86_64.rpm

Some users of rhel4 based systems may find that they have an older version of apt-get installed. And that will barf on the correct syntax for the source installed by this package. Try converting the line in /etc/apt/sources-list.d/rpmforge.list to something like...

 rpm http://apt.sw.be redhat/el4/en/i386 dag 

E: Dynamic MMap ran out of room

If you get this error chuck this in the bottom of your /etc/apt/apt.conf:

APT::Cache-Limit 50000000;

Per Liz's post here.