GoClass is an interesting, free app for teachers that allows them to create lesson plans, poll students and disseminate information from a single app. Currently, registration is free.
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
This free app provides instant access to the Common Core Standards. Not sure what to do with it, but it could be useful from an administrative/lesson planning stand point.