Apart from ipa are there any other good tools out there for centralised user auth?
I am currently testing LDAP (openldap) combined with nss_ldap, configured with authconfig.
I would start by testing IPA. Redhat is building out a set of enterprise management tools which include cobbler and spacewalk; I would think IPA will eventually be integrated into their mgt tools.
That said, if you want to use Ldap + Kerberos, here are two good howtos: http://aput.net/~jheiss/krbldap/howto.html http://www-theorie.physik.unizh.ch/~dpotter/howto/kerberos
The "current" centos rpms for Ldap are quite old; you should consider rebuilding the latest fedora rpms for your system.