The Peoria Plague is a great radio drama from (I believe) 1972. Not only is it well-executed, but it most likely features the first modern (that is, non-voodoo) zombies in audio drama history. It's clearly an homage to the War of the Worlds, and there are some some relatively minor sound quality issues, but if you're a fan of old-time radio, modern audio drama, and/or zombie films and fiction, it's totally worth an hour of your time.
I posted a link to the recording here a couple years ago, but it's been down for a while. I love sharing obscure gems with people, though, so it's back up, and it wants you to listen to it. Download it here.
And while you're at it, check out my full review of The Peoria Plague in my Dead Air segment of the Mail Order Zombie podcast. It's in this week's episode, #127, right around the 42-minute mark.