My son is reading Tom Sawyer for his 7th grade English class, and his teacher told the class they could also listen to it on audio and gave them the web address for Free Classic Audio Books.
This site is so cool! Just as the name suggests, it includes a bunch of audios of classic books, available for free (notice there are multiple pages). Lots of these books are ones that are commonly assigned for English and Literature classes for middle-school, high school, and college students. Thanks for the tip, Mrs. Hall!