I remember using Dragon NaturallySpeaking many many years ago on my old Windows (that's right, I said it) machine. I recall it being a pain to use and it didn't work very well. Well, it looks like they've really improved the software and have made a nifty little iOS app called DragonDictation. It's a free app available in the App Store that allows you to speak anything and it transcribes this speech to text for you. It does a surprisingly good job. When you've said everything you want to say just hit the e-mail, text, copy, Facebook or Twitter button to send the transcription to the corresponding app. The only cons about the app that I find are that it doesn't do punctuation so well and that it's not already integrated into the iOS.
I would for sure recommend this to anyone who types emails on the iPhone, or likes to make voice memos. At the very least, it's a fun app to try and it's definitely going to stay on my iPhone. In fact, this entire blog article was written by using DragonDictation for iPhone!