Next year i am going teach much more with iPad. Pdf annotate tools let me read, comment and give better feedback for students essays. What i like most is possibility to speak my essay feedback in to the document. For that task im using Notability and iAnnotate PDF tools.
I also like InstaWeb which allows to make PDF-files of any webpage. Camscanner changes photos in to PDF-Files.
Check also this out!
Ultimate guide annotate pdf files on the iPad
InstaWeb - Web to PDF converter
PDF max pro
PDF expert - fill forms annotate PDFs
PDF annotation apps