Pollyanna, by Eleanor Porter, is a great classic that my kids and I enjoyed listening to at Librivox during the summer. I love Pollyanna's attitude about finding something to be glad about in everything, and how this endears her to everyone around her.
I read it when I was a kid, and remember being unimpressed, but my girls all loved it. They like a lot of things that I like now, and didn't when I was young. Not sure why exactly that would be ... something to do with homeschooling, maybe?
Anyway, I highly recommend the book. And Librivox, also. Librivox is a site full of public domain books that have been recorded by volunteers. It's all free, has tons of classics available to listen to, and some of the readers are very good.