I have a new app in the iOS App Store named Jot.
It’s dead-simple. When you start it, it immediately brings up a new mail with the To: and Subject: fields pre-populated, so you can immediately email yourself (or whomever you choose).
This was something I developed for myself since this is a task I do all the time, when I need to tell Future John to do something. This video demonstrates how much time Jot can save if this is something that you do frequently:
It’s free and available now in the App Store.