
Alright, follow me on this one.
iAnnotate is one of the most popular PDF viewing and annotation iPad apps in existence, and it's on sale for $1.99 right now to "celebrate" the back to school season. That's 80% off its regular price ($9.99). The deal is only good until September 13 (12pm CDT).
iAnnotate bills itself as "the most powerful PDF annotation application for the iPad" that includes an "intuitive interface" and a "comprehensive set of features" for taking notes and annotating documents.
Download link:
iAnnotate PDF