Wondershare lets you edit PDFs from a Mac. It is less expensive than the full version of Acrobat. A great classroom example came from an EdTechTeacher summer workshop participant. She created a Wordle, which she saved as a PDF. Then she inserted a QR code into it that linked back to additional information on her blog.
This note taking app includes multiple pen and highlighter tools and functions much like a paper notebook. For $5.99, it offers a lot of organizational and editing tools. Additionally, Noteshelf exports notes as PDF or image files to either Evernote or Dropbox.
Shakespeare in bits provides animations as well as the text with reading tools to understand Shakespeare. This one works for Romeo & Juliet, but there are also editions for Macbeth, A Mid Summer's Night Dream, and Hamlet. While it's $14.99, it does come under the VPP so it comes as the same cost as the book.
Though $7.99 seems steep for an app, not only does this one allow you to edit Office documents (same as Pages, Keynote, & Numbers), but it also lets you work on Google Docs.
The Audio Memos app, mentioned here at Free Technology for Teachers, is a great audio recording option. The Free version is a bit limited, but the Pro version ($9.99) includes editing tools.
YouTube's response to Vine & Instagram, MixBit allows you to shoot, edit, and post video from your mobile device. Technically an iPhone/iPod app, it would work on iPad.