This site provides a very good information about The Mercury Theater on the Air from the 1930s. Teachers and student teachers with whom I work are delighted with the selection of old radio dramas that are found here and many get ideas for K-12 classroom lessons from listening to selected shows. The 1988 Leonard Maltin interview with surviving members (found at the bottom of the page under the Theater of the Imagination link) provides a solid cultural and historical context for radio dramas in America in the 1930s. I would rate this site a 5 instead of a 4, but some days the server where this site is housed is down. The actual content of the site is excellent.
You need RealAudio or RealPlayer or a MP3 Player to effectively use this site. The old time radio dramas are available in streaming audio format or can be downloaded for RealPlayer or MP3 players.