Question: Are there any half-official repositories for CentOS 5 with Python 2.7?

EPEL provides only Python 2.6

Answer: 
I made an RPM for this a little while ago. You can find the source RPM here

<ftp://ftp.pycopia.org/pub/python/RHEL51/python2.7-2.7.1-1TH.src.rpm>

Just do the usual `rpmbuild --rebuild ...` to create the binary rpms. It does not interfere with the installed 2.4 version, it coexists with it. but you do have to put the specific version in your scripts: `#!/usr/bin/python2.7`. But if you use setuptools invoked with that version then it happens automatically.
You can try my build adapted from Fedora 16:
<http://ftp.srce.hr/redhat/test/el5/x86_64/>