Cork board type app that allows students to organize research or a project on their ipad. The free version allows for one board. Online, collaborative version would be Wallwisher
eBackpack offers storage and collaboration features to individuals, classes, teachers, and schools. Now, there is an iPad module to help manage workflow and student portfolios. The pricing is quite affordable.
We use VoiceThread in a lot of our EdTechTeacher workshops as it is completely web based and now includes an iPad app. As a tool, it can create digital stories, be used for foreign language exercises, or support the creation of collaborative study aids. This library is a database of articles about successful VoiceThread projects.
This site provides both a social network for your class as well as iOS/Android/Facebook apps to support learning outside of school. Unlike other study apps, this one encourages teachers and students to collaborate and engage via their Study Hall social network