The iTunes Store offers downloads of PDF Forms for iPhone, iPad, and iPod Touch for free. That's a $9 price drop and the best deal we could find. It allows you to fill, sign, and annotate PDF forms and documents.
Orbitz for iOS or Android cuts $25 off your first hotel booking via coupon code "DOWNLOAD25". (A 2-night minimum stay is required.) That's the best dollar-off discount we've seen for hotel stays from Orbitz this year.