Spaceship radio at http://www.spaceshipradio.com/ has been playing public domain 1950's radio drama's. These shows are really entertaining. My favorite so far is the production of Green Hills of Earth based on the story by Robert Hienlien. This harkens back to a different age of entertainment when the words and sounds would construct a picture in your head. Besides playing old radio shows Spaceship Radio is also in the process of producing new radio drama's.
in the new radio show vein I recently found Star Trek: Pioneers done by the people at http://www.darkerprojects.com/ . This is just one of many star trek fan productions. There actual video series out there being done by folks with an almost proffessional level of quality. But Star Trek: Pioneers is a well produced radio drama with good sound and decent voice cast. It is entertaining to listen to on the way to work.
Overall i hope more people do this sort of thing. I know I am still toying with producing my Dawning Star podcast soon. Maybe Atlanta Radio Theater could start doing a podcast.