GoodNotes

GoodNotes lets you take handwritten notes, sketch diagrams, mark-up PDFs and organize them on a beautiful bookshelf. Turn pages with a swipe, highlight or add notes to any page, and share your notes with anyone. GoodNotes will automatically save your notes and has full backup function to prevent data loss.

Price: $3.99

Platform: iPad

More info: http://itunes.apple.com/us/app/goodnotes-notes-pdf/id424587621?mt=8