At TeachThought, we often provide lists of digital resources, and many of them are apps.
Apps for struggling readers. http://www.teachthought.com/apps-2/50-popular-ipad-apps-for-struggling-readers-writers/
Apps for struggling writers. http://www.teachthought.com/apps-2/41-resources-tools-and-apps-to-improve-writing-skills/
Apps for project-based learning. http://www.teachthought.com/apps-2/10-apps-for-more-organized-project-based-learning/
Any while many of these apps are for students, the following list of apps from Sam Gliksman can be considered for both teachers and students, and an excellent foundation slew of apps for any 21st century teacher. From GoodReader and Slide Shark to Printopia and Air Display, all fill different niches of 21st century learning, and the many possibilities the iPad affords."
Via John Evans