One of the best PDF annotation application for iOS ipad
Lowest price its been for a while.
Price goes live Thursday US time for 1 day only
4.5/5 star rating with ~ 9000 reviews
This app has never been FREE either
Source: http://www.branchfire.com/freeiannotate/
Enjoy
Great price. I've been using this for writing notes on lecture slides and textbooks.