mirror.chpc.utah.edu has all CentOS versions and the DVDs. It is open to anyone. It is connected to both Internet2 and NLR (National Lambda Rail).
mirrors.rit.edu hosts the same and is on I2.
Being on I2 I can poke a hole in the bandwidth limiter for you too (I have yet to figure out the BGP magic to make that automatic)
Paul Mezzanini