I have seen many questions where users are not sure whether they have a specific package suggested in a solution or perhaps even request alternatives (to avoid installation) or want some information on how to install it. As such, I typically include the CTAN link with when listing packages used, since the "Getting it" link will provide ways of installing packages if not installed already:
What I'm interested in is to know which packages are included in a default installation for some distribution (across the many distribution that exists...). Almost like a
\listfiles for an MWE containing all packages in the default distribution, if such an MWE could ever exist. For example, if someone (say, a new user) is running the Basic Installation of MiKTeX 2.9, how would I know what the difference is between it and, say, the Complete Installation? And what about different versions, say MiKTeX 2.8? Or TeX Live 2010 and 2011? What about MacTeX?
Perhaps there are sources scattered across the Internet I don't know about. Ideally, something like a historic archive similar to @MartinScharrer's Automated Mercurial Repositories of CTAN.