I've also had good luck with "scannable" in the past (acquired by evernote, but still works without evernote). One nice thing about their UI is that as soon as

I've also had good luck with "scannable" in the past (acquired by evernote, but still works without evernote). One nice thing about their UI is that as soon as it gets a good lock, it acquires and processes the image, and then moves on to the next one, making it really easy to quickly scan a stack of papers into a single PDF.