Commoncraft (who call themselves "social design consultants") has a series of very well-produced short videos called
the commoncraft show that demystify "in Plain English" concepts that befuddle clients such as
RSS,
wikis and
social networking. They are short, funny and extremely informative.
I got to this site by meandering through a Jared Spool article on
Building an Envisionment which talks about creating the right presentation to illustrate a concept that will guide or inspire your project. Also worth a visit and good read.