RedHatEnterpriseLinux is
RedHatTheCompany's enterprise grade linux. It is more stable than Fedora but is similar. It is the current "standard" linux distro. Most corporations that use linux use it. It is good for new users who can afford it. It is a ripoff compared to most linux distos. I do not recommend it; use Mandriva or Debian instead.
There is a free distribution called
ScientificLinux which is based on the same source code.
See also
FedoraProject,
RedHatLinux
CategoryLinux