SciFi/SyFy used to have some awesome audio drama called Seeing Ear Theater on their website. They eventually stopped doing them and took it off their site. Now you can find a description of a good deal of it here:
http://www.sffaudio.com/?p=19883 , but the links no longer seem to work.
You can download or stream most of them here for free:
http://otrarchive.blogspot.com/2010/...r-theater.html
Some of them are excellent. Some of my favorites from that series:
Snow Glass Apples (Neil Gaiman penned Snow White audio drama)
Neil Gaiman's Murder Mysteries (a really great mystery noir set in heaven’s City of Angels before the fall, where the first crime has been committed)
The History of the Devil( penned by Clive Barker)
City of Dreams (a J Michael Straczynski series that was supposed to go for 13 episodes, but only eight got made. Each episode is stand alone, though.)
Tales From the Crypt ( audio dramas from the Crypt Keeper)
There is also a group called GraphicAudio that does some very audio drama like versions of a number of books.
http://www.graphicaudio.net/
There are some very well done ones on there.
I also enjoy Wormwood:
http://wormwoodshow.com/
"Doctor Xander Crowe was a formidable psychologist until a terrible tragedy sent him spiraling down the dark pathways of the occult. Now, a strange vision leads Doctor Crowe to the hidden town of Wormwood, where shadows lurk in every corner and evil stains the souls of the inhabitants. Welcome to Wormwood."