I'm more of a reader than a listener, but I do have some recommendations:
A Tale of Despereaux - A great fairy tale fantasy about a mouse, a rat, a maid, and a princess. Graeme Malcom's voices and accents for the different characters are absolutely amazing.
Harry Potter - Jim Dale narrating all the Harry Potter books. Enough said.
Now if you like Star Wars, I heartily recommend the Star Wars Radio Drama. In the 80s, Lucasfilm partnered with NPR to adapt the original Star Wars film to 13 half-hour long episodes which were broadcast weekly nationwide. Mark Hamill returned as Luke Skywalker and Anthony Daniels played C3PO. The rest of the cast was a group of very talented voice actors who sounded similar enough to their movie counterparts to make it believable, but different enough to allow them to make the roles their own (in fact, to this day I prefer Ann Sachs's Princess Leia to Carrie Fisher's). A lot of scenes were added and expanded, giving the story a lot more depth and foundation.
A New Hope was very successful, so Lucasfilm asked Brian Daley (the scriptwriter for the first 13 episodes) to adapt The Empire Strikes Back to 10 half-hour long episodes. Hamill, Daniels, and the rest of the radio cast returned for the production, and Billy Dee Williams himself reprised his role as Lando Calrissian.
I'm afraid I can't really recommend Return of the Jedi though. It was made in the mid-90s, long after Empire and it's only 6 episodes long. As such, it doesn't add a lot of new material to the story; it only stretches things out and makes the story tedious. Hamill and Williams didn't return to play Luke and Lando, and their replacements didn't really deliver (Lando's actor in particular was terrible). The only real highlight is hearing the radio cast again.