Openlearn, a free learning website, has lots of material, usually quite short pieces and a very great variety. Just go into internet explorer and key in 'openlearn' and you should get to the OU open learn site. It may ask you for a password but you don't need one to access the materials, since it is an open access site.
They are mainly specially made and linked to TV programmes co-made with the BBC, hence the rather assorted collection assembled there.However, there are some useful pieces eg. There is a great piece on statistics by Hans Rosling called 'The Joy of Stats' which you can find by keying in this title.
The learning space website has got longer, more academic units on it extracted from OU courses and is more useful for teaching purposes. It includes four extracts from K311 course (the previous version, not the newly rewritten one, however). The extracts are: 'public health; an introduction' (which has a useful video of community work in Coventry in it); 'epidemiology: an introduction', 'public health in community settings' and 'factors that influence health'. You can find them all by using the same route as above – generic site access at http://openlearn.open.ac.uk and then search by these titles.