Where can I find up to date RPMs for different versions of Redhat Enterprise Linux? Specifically I'm looking for an Apache RPM. Normally I would turn to: http://dag.wieers.com/rpm/packages/ but they don't seem to have any RPMS for apache.
You should get packages for RHEL from Red Hat Network. In the interest of maintaining utmost integrity of packages, Red Hat only patches packages with serious bugs (ie, security), and backports these packages to the main version of the specific software.
If you want to run the latest and greatest bleeding edge Apache, you're pretty much on your own. Red Hat won't provide any support for packages that were not installed for that specific RHEL version from RHN.
While packages for other distributions like Fedora Rawhide may install cleanly, those packages were not "blessed" for RHEL. If you're running RHEL, stick with the packages provided by RHN.
Fedora generates missing but compatible packages for RHEL and they host them in a repository called EPEL (Extra Packages for Enterprise Linux).
At a glance I don't specifically see Apache RPM's in there but EPEL is definitely worth adding to your list of repositories for other software. I couldn't stand to use RHEL/CentOS without it!
By apache do you mean the web server?
If so, it's not called 'apache' in RHEL. Try:
yum install httpd
Have you looked at Fedora Rawhide? They have 2.2.9 available. It should install cleanly on RHEL.