If you are looking for a way to read lots of blogs and web sites from your iPad or iPhone, Google Currents could help. It is an RSS reader that saves content for off-line reading.
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 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.
Though an older post, this is still a good starting point for integrating QR codes into the classroom. The Mobile Native is a great blog for integrating mobile devices and focuses on younger students.
This is a great blog post from edSocial Media regarding using apps as sources. As more schools move towards iPad integration programs, this is increasingly going to be a challenge.