I'm still keeping my dual-Atom CPU Multi-Boot Mini-Server up to date, so I was pleased to see the release of CentOS 5.4 a week or so ago. This is known as the Community Enterprise Operating System, and although it is based on a fresh compilation of the Red Hat Enterprise Linux sources, it goes far beyond being just that. It includes more and better packages, improved updating and repositories, and much more. Although this is a minor release step (5.3->5.4), there are some significant changes and improvements. Check the Release Announcement for general information, and the Release Notes for a detailed list of new and updated packages.
If you want to take a look at CentOS, this release has both i386 and x86_64 LiveCD downloads. One small word of caution, though. Unlike most other distributions, you can not install CentOS from the LiveCD, for that you have to download the DVD distribution. I installed the 64-bit distribution on MMS today with no problems.