A free online e-book for learning about and how to use a variety of Web 2.0 tools including Diigo, blogging, wikis, Evernote, Flickr, Glogster, Jing, Prezi, Ning, SlideShare, Twitter, and VoiceThread,
Good variety of sites to use not just in the summer but all year. Check the list, and you will find one or two to use right away. I tried the Spell with Flickr one.