XFS Rpm for RedHat
The CentOS project has prebuilt xfs kernel modules as well as xfsprogs rpms for CentOS4 and CentOS5 in the CentOSPlus repository.
These originated from Eric's RPMS, see also his site for RHEL4 and RHEL5
When in doubt, using the Centos RPMs is probably the best approach. These can be used with RHEL as well, but of course this is not supported by Red Hat.