Mightybook is a pretty cool website, not really a Web 2.0 too, but a great website that has quite a few children books that are read and animated for students. There are many poems, songs and short stories that students would love to see and read. There are many other activities that students can participate in as well, such as educational puzzles, art and games.
Unfortunately you need to subscribe to get all of the content for an OK price. I am a big fan of free content, but some content is worth buying and Mightybook does well at producing valuable educational content The material also spans across grade levels K-4.
Below are some screenshots of what you might see when using their site.