I've heard good things about the flip-pal. It runs about $150 and doesn't need a computer at all to work. I don't personally have one and have gone back and forth on if I really need one or not.

As for PDFs, I use them just as much as I do photos. I scan all of my documents as PDFs, it makes it easier to keep them all together if there is more then one page. This works well for wills and probates and such.