This is my latest fine and already a fav! We Give Books has several children's eBooks that you can use in your classroom. One of my new favorites is Goodnight iPad, similar to the book Goodnight Moon.
These are all free eBooks.
This site has eBooks for young kids. Some of the stories are unknown but they also have books from the Arthur series.
Tumblebooks is a great resource for eBooks for kids. Unfortunately, it does cost money. However, there are readable books, audio books, and even books that read to you! Most books also have quizzes or games associated with them. Our school purchases this program so our kids can use it at school and home. The kids absolutely love it! They are also more and more nonfiction books too.
This is actually a link to an app for iPad or iPhone. Dr. Seuss is one of my favorite authors and I thought this is a great resource for classrooms using iPads, especially for the younger kiddos!
This is actually a site of videos where actors are reading well-known books. I like to use these from time to time for a reading lesson when I want to put a little novelty in my lesson.
Barnes and Noble has some books online read by authors or actors. This is great for younger kids!