I've written before about how I got involved in listening to audiobooks while doing my morning run on the elliptical trainer.
The first book I listened to was the 30-hour book John Adams, on which the HBO miniseries was based. When that was finished I listened to Longitude, about the 18th century search for an accurate method of determining longitude at sea; I just finished that book this weekend.
I've downloaded Augustus and will spend the next couple weeks learning about the Roman Empire's first emperor. If I listen to it only while on the elliptical I'll be listening to it into March!