Please add the following mirror to your advertised mirrors list:

http://mirror.anl.gov/

We are providing a complete CentOS mirror, synced every six hours (this can be modified if desired). Details can be found on the page above, but the URLs for CentOS access are:

http://mirror.anl.gov/pub/centos/ ftp://mirror.anl.gov/pub/centos/ rsync://mirror.anl.gov/centos/

Hardware and network details here: http://mirror.anl.gov/#about

Cheers, -Brian