I came across this great link via The MedRom Forum.
It's a series of podcasts by Mike Duncan titled "The History of Rome". At the risk of repeating the original poster on MedRom, each audio file is approx 15-20 minutes long and about 8Mb in size. Due to time and bandwidth constraints I have only managed to download 1 of the 24 (at time of writing) and I must say the sound quality is excellent.
Here's the link: Mike Duncan's "The History of Rome"