It's been a while, but I remember The Stand audio book being great on my first road trip across the US. Also, I wouldn't classify them as "great", but I've been hooked on the "We're Alive" zombie podcasts for a while now.
John Glover reading Steven King's Jerusalem's Lot.
Wayne June's Lovecraft readings.
Not sure If the following are great, but worth a shot...
Scott Sigler's Podcasts... if you like gore.
Harold Roberts reading the novelization of Alien, IF you can find it.