CentOS is 100% binary compatible with RHEL, but currently the most up-to-date version is 5.6. If you want support for newer hardware (wireless, bluetooth, web-cams, and such) then try Scientific Linux 6. It is also a RHEL clone, but at version 6 (latest and "greatest"). I am using it now, and am quite happy with it. Hardware that didn't work with CentOS 5.x does work now.