iPad Academy is a great blog, and to celebrate it's 50,000 visitors, they posted this list of "70+ starter apps". It's a great resource for getting started with iPads.
While the Google Presentation in this post is intended for working with students who have hearing and visual impairments, some of the apps are valuable for an array of different learners.
This blog post lists several apps to use for mobile grading and keeping a grade book on an iPad. It is important to note that some Student Information Systems - such as Pearson's PowerSchool - have developed apps that integrate directly with the computer-based grade books.
This list comes from Teacher Reboot Camp. The suggested apps provide multiple ways for students to interact with various aspects of stories: plot, characters, setting, etc.
A great list of apps for students with special needs. It includes a description, cost, and links. Thanks to Meg Wilson at iPodsibilities for Tweeting this one out.