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.