PDF-XChange Editor - The smallest, fastest, most feature-rich PDF editor/viewer available
Scanbot - Scanbot is a mobile app that allows you to use your device's camera as a document scanner. The app is capable of scanning a large number of source materials, and it can handle QR codes as well.
ScanTailor - Scan Tailor is an interactive post-processing tool for scanned pages.
Scanner Pro - Scanner Pro turns your iPhone into portable scanner in your pocket.
Briss - Cross-platform application for cropping PDF files in a simple and fast way via a GUI.
Genius Scan - On The Go.