We Give Books
One of the best-looking online free book sites, We Give Books offers about 200 great titles of kid’s picture books to read. The best part - when you read the books online, you can help to support one of the charities too! Look under their 'Classics' section to find "Frosty the Snowman", "Madeline", "Miss Rumphius" and "The Little Engine that Could"! This is a wonderful site for young kids and also beginning readers as they also offer some ER (easy reader) selections.
Books Should Be Free
Maybe your kids enjoy listening to books on the car ride (especially good for kids who can't read in the car). Books Should Be Free offers a nice selection of audio and text versions of Children's Books, again many of the classics. You can download them to your iPod to listen to on the trip!
They also have ebook formats for Kindle, iPad, iPhone, Nook, Sony Reader and laptops. Here's their page for Peter Pan by J.M. Barrie so you can see all the different options.
Robert Munsch's Website
The author of amazing books like "The Paper Bag Princess" and "Love You Forever" has 50 of his great children's books online - in both audio and download formats! This is a beautiful site where anyone can find more than one book that they'll enjoy!
A new site that I stumbled across, Oxford Owl has a nice variety of books for kids ages 3 - 11 that the computer reads to them. It would appear that you'll need a laptop and flash player to see the books. If you choose the ones marked with an 'e' they are free books.
I really like some of the features of the site - it offers activity ideas that go with the books and you can turn pages to see the illustrations with most books. Also, the voice of the narrators seemed very nice. With some books in the youngest (ages 3 - 5) and oldest (ages 9 - 11) age groups, there aren't any words that show up on the screen, you only hear the story. Nevertheless, a good site if you're looking for access to stories (both fiction and nonfiction) for a variety of ages.
You will need to create a login for yourself, but it is well worth it.
You can download some nice kid’s book apps for the iPad and iPhone from iTunes. MeeGenius Kids' Bookslooks to have a nice variety of free books available. Open Culture has a list of 450 free audio books, many available through iTunes. These will be chapter books and classic books - great for read-aloud or summer reading for your teen! Titles like "Hans Brinker", "Alice in Wonderland" and "Swiss Family Robinson" will appeal to a wide age range.