ftp-linux.cc.gatech.edu is a decent one. When RH7 first came out they were limiting bandwidth, not sure if they do that all the time. Not like Tech doesn't have bandwidth to spare, I guess they just don't want to use it all on redhat geeks.
But just the other day, I downloaded both ISOs in about 70 minutes each from ftp.redhat.com. I guess I got lucky and was able to connect.
A neat tip, try European mirrors in the evening time, it's the middle of the night over there and most folks are asleep so you should be able to get decent throughput.