lammert - 9:09 am on Jan 7, 2011 (gmt 0)
The look and feel of Fedora, RedHat and CentOS on the command line level is almost the same. They all have the yum command. Packages on RedHat and CentOS may be a bit older in version, but they are good maintained and very stable. Fedora has also a very short update and security fix cycle, much shorter than the expected life span of your hardware. That is less than ideal for a server environment where you need security fixes and often can't afford upgrading to a new version in between. I would therefore go with one of the other three distro's.
Debian is different on the command line level than Fedora. Except for the available technical support, Centos and RedHat are virtually identical. My advice would therefore be Centos.