WordSift was very interesting. It can help the students with vocabulary and there is even a visual thesaurus which makes a weblike visual of the most common words. You can also put in words for the thesaurus to web out. You do have to pay a fee for use of the visual thesaurus. It only let me play around for a few minutes. Here is the link. http://www.wordsift.com/visualize.
Storybird is interesting in that students are able to create a book with artwork on the site. Students would be able to use information from class to create a book for kids or their peers.