I don't think that there's likely to be that many preachers here. It's not that common a profession. You'll probably find more iPad users in a preacher forum than preachers in an iPad forum.
There are more here than you know.
To the OP:
As you know, sermon prep is a highly personal process and obviously what works for one teacher won't work for another. But I'll share a little of what I do on the iPad:
First, I never have, and most likely never will preach directly from an iPad. It isn't a technical issue, it isn't a spiritual issue, it's simply my personal preference. I prefer the freedom of having my sermon notes (8.5"x5.5") tucked in my Bible and being able to easily put it down and pick it up. (I tend to wander away from the pulpit)
I have a full-time job in addition to my pastoral responsibilities so while sermon prep primarily happens at my home office, I always have a device with me that allows me to "move things along" throughout each day during the week. So virtually all the software that I use is cross-platform in some form or another.
Having said that, here is a list of the apps that I use and why I use them....
SimpleMind (iOS/OSX/Android) - Cross-platform mindmapping software. I use it to capture my thoughts and supporting verses for the central verses that I'll be teaching on. The central node is the scripture reference (the text annotation is the text of the verses). From that visual, themes and points of interest pop out.
SimpleMind supports Dropbox so my mindmaps are stored and synced there.
Notesy (iOS),
nvAlt (OSX),
Draft (Android),
ResophNotes (Windows) - all with
DropBox. I find plain text (with occasional markdown) to be ideal for distraction-free note taking. This is where the preaching points are taken from the mindmap and expanded with greater detail. All of these files are stored/synced in Dropbox. I used to use EverNote, but it has become bloated over the years.
LOGOS (iOS/OSX/Android),
eSword(OSX/Windows),
iBible-Study HD (iOS),
Bible (LifeChurch.tv) (iOS/Android): I use a variety of these tools because I have many resources for each that I've received over the years for free or at significant discounts. I still find eSword version 8 t be the best tool for me.
Pages '09 (OSX). I use this to create my final set of notes that I teach from. I prefer to have a mix of printed and handwritten notes so I took the effort to create a font of my handwriting. This allows me to type everything and then manually add last-minute notes that are consistent with what was already written.
I also use Pages '09 for the teaching outline that is handed out to the congregation.
If Apple was to ever upgrade Pages to anywhere near the functionality of Pages '09, then I would upgrade to that and take advantage of Pages for iOS.
As it is, I have created some nice templates that I use for both teaching notes and outlines and with custom styles, it is pretty simple to roll them out.
there may be another app or two that I use that I've forgotten to mention, if so, I'll update this post.
hope this helps.