The iTunes u App now available from the app store is FANTASTIC.
It is used to download courses from an amazing number of universities and other learning institutions - and the majority are absolutely free.
The courses are a mixture of videos, text documents and PDF files, although some also contain links to online files. The learning disciplines are very varied, and anyone using the app should find something of interest.
As I live in the UK I naturally looked for courses from the Open University. There are dozens of them, and already I have subscribed to 13, together with 2 from Yale University.
The only gripe I have is although videos play within the app, PDF file still open (and are saved) in iBooks.
I can thoroughly recommend it.