JPL sponsors many different seminar and lecuture series, including the von Karman Lectures Series, the Earth and Space Science Colloquium, Science 101, and many other events -- some of which are open to the public.
List of Seminars:
http://technology.jpl.nasa.gov/newsandevents/seminars/
List of Seminars:
http://technology.jpl.nasa.gov/newsandevents/seminars/