ClearOS is a CentOS-based alternative. However, the devs are in mid-swing for pushing out ClearOS Enterprise 6.1 (Core is just a recompilation of CentOS) and it's still in beta (and I expect it to be for a while). I currently use ClearOS 5.1 (based on CentOS 5.5 or so) and it's decent. You lose some features (like the newer virtual IP implementation in the newer kernels like ClearOS 6.1 is based off of) but it's stable and the WebUI makes it all easy, but the underpinnings are still widely available software with standard conf files so it's easy to do advanced configurations from the shell.