Create a custom repository of your packages and point all the machines in your cluster to it? If it is CentOS or RHEL just add a new repo to /etc/yum.repos.d. If you are upgrading system repos then just set the priority of your repo to be higher. Of course this implies that you have successfully rpm-fied your packages. We did that to all our packages and configuration.
If you run the Red Hat family (Fedora, CentOS, SL, whatever else) you could also run Spacewalk. Machines periodically check in and get config files and packages that it needs. If you configure it to do so you can also push.
At my last job we ran Spacewalk on our Koji box. Koji will let you build packages that you can then put in your repo to yum install.
+1. Yum and apt and the like are awesome for individual machines, but pull based. Spacewalk and RHN are centralized push, which you need for any decent amount of machines.
