Here are 2 that we have really enjoyed (The kids begged me to turn it on even if we were just driving the 2 minutes to get the mail):
Mr. Popper's Penguins by Richard and Florence Atwater Read by Rick Sullivan.
My kids are animal lovers (and so am I, hence the mini farm we have going on around here). We all had a good laugh at the antics and inconvenience of having 12 penguins to care for.
The Wonderful Wizard of Oz By L. Frank Baum Read by Brooke Shields.
I had no idea that Dorthy and her friends went on so many more adventures in the book than in the movie. The book also ends a smidge different that the movie as well. Definitely worth the listen.
For some other audiobook ideas head on over to Homeschool Creations and see what they've been listening to as well.