The favourites at the moment:
The Hobbit and The Lord of the Rings trilogy, the BBC radio collection/dramatization. I bought them from Amazon, second hand.
The Story of the World. We don't 'do' the Well Trained Mind (although my kids do have quite well trained minds ;)), but I was looking into buying the audio books, because they looked good. They were quite expensive, so I'm glad one of my friends had it and I could borrow it. Anyone else who could lend me the next Volumes? ;). We listened to the first cd yesterday evening, and I'm going to make sure I'm there when the boys are going to listen to the next one, because it's very interesting!
Gombrich's 'A Little History of the World'. We have done part of the book in Dutch, but never completely finished it.
Boaz and Levi really like the Beatrix Potter stories. Ours are in Dutch, but you can also get them in English....
And of course the Julia Donaldson collection! The favourite cd is the Gruffalo one..
What's your (kid's) favourite audio book?