The only place I've found that consistently delivers excellent audio series is The Teaching Company.
http://www.teach12.com/They have award-winning professors that design courses specifically for an audio format. Some of them are absolutely amazing! (I've loved the "How to Listen to Great Music" and "US History v2". Awesome teaching... I can actually stay focused on them for hours at a time!)
They're a bit light on the science side... more history and philosophy, but definitely worthwhile. (It's difficult to translate science / math as effectively into an audio format.)
A lot of "audiobooks" just don't work very well. They're better read than listened too.