There's not currently such a list. One problem is that at some point we may stop making atomic releases. What I mean by this is that various packages will get released on their own (dotLRN is an example, though parts like the new portals package will get mainstreamed), new versions of packages will get released even when the core's stable, etc.
This makes a central list more difficult to keep.
But ... we will eventually be setting up a smarter site with the OpenACS 4.5 download package. This package includes a summary page of everything available under a particular repository (say, the OpenACS 4x repository).
This is one more reason to try to find the resources to push forward with the implementation of our new openacs.org website ...
