This App allows users to annotate PDF files. One can insert comments, questions, signatures, etc. Teachers are using it for running records when the leveled texts are put in PDF form.
Using IAnnotate you can add comments and voice to students' work, even pdfs. It has many features. App for both Android and iPad. $9.99, a bit pricey but looks to be worth the money.
Pdfs--A Call for Change, which examines the achievement gap for African American males. Also, Beating the Odds, which looks at student performance on NAEP data (2006-2009)
mp3 collection of 'free' stories and poems; can search by author, title, reading level, content. All have PDF of passage so can be read as listened to.