I've done some ipad trainings across our district K-12. We've mainly focused on what function do the students need to perform, not so much on a specific app. Our motto is Gather, Build, Share. So if students are gathering information, they could use QR code scanners to quickly get to a website, online bookmarking sites like Diigo or Delicious to save their links, or Evernote to capture ideas... but the emphasis is on developing research skills to gather info. For Building, we focus on apps that allow them to work with the information they've gathered, such as Popplet to connect and map ideas. Or PicCollage, which lets them find real world examples of what they are learning. Finally, for Sharing, we look at tools like Educreations (whiteboard software) where students can record their voice and create a simple presentation. We also go over strategies for teachers to collect students' work, such as sharing on Dropbox or entering a link to their presentation on a Google form.
I hope this helps a little.