Where can an academic put their lecture slides for posterity? I was recently asked this question by an academic colleague and realised I didn't know the answer.

Academic X is about to retire from a computer science department and has a set of undergraduate lecture slides he is very proud of. He would like to put them online so they are available to the world. Where can he put them?

The arXiv is not suited to hosting lecture slides.  There is wikibooks which is a possibility but the quality isn't great and it is in Wiki markup I believe.

The university he works at has no permanent location to host retired academics' work sadly.
Archive.org (not to be confused with arxiv.org) aims to be the world's library. According to its FAQ,


  The Internet Archive focuses on preservation and providing access to digital cultural artifacts


It cites the destruction of the Library at Alexandria as the kind of loss of cultural heritage which it aims to avoid, so preserving an academic's teaching material should be perfectly aligned with their goals.

The FAQ also has a large section on uploading content. I suggest you pass that URL along to your colleague.