I just released a set of scripts that come in handing when creating clean images for virtual environment, heck you can even use it for cloud images.
What they do is:
- clear all the logs
- clean up the networking scripts, because the normally get references to the mac address in CentOS
- clean up the repository files
- in some cases create a root user
There are scripts for: CentOS 6, Debian and OpenSuse.