This has quickly become one of my favorites, making its way to my home screen.
Gabe Weatherhead from Mac Drifter wrote a great overview.
DEVONthink for iOS is a full featured, secure document manager with terrific capture tools and a really powerful PDF editing option. It supports simultaneous sync with several different services and adds encryption on top. I like it better than Evernote, Apple Notes, or OneNote. It costs $15. Buy the IAP to get better sync and PDF editing. It’s changed how I use my mobile devices.