Dragon's Naturally Speaking speech recognition software for windows is pretty amazing stuff. It basically types what you say, and is amazingly accurate.
Well a bit of that magic is making its way to the iPhone in the form of a dictation application. You talk, it dictates, and gives you the option to send the text to an email or text message. The application has some small issues, but hey it is free. Just search for DRAGON DICTATION in the app store.