Thanks to Todd Deshane for linking me to Stacklet (http://stacklet.com), a repository for Xen DomU Images. The site currently has images for CentOS 5.3, Debian (Lenny), Fedora 10, Gentoo, Mandriva, Slackware, and Ubuntu 9.04. There is also a forum associated with the site if you have any questions.
If you try any of these images, let the community know how they work so everyone can start leveraging the great efforts from the Stacklet team.