Vlingo allows you to dictate speech to txt, and it's free. It works with messages, email, and initiating phone calls. I use it all the time and it seems to work very smoothly.
I agree with everyone else recommending Vlingo to compose and email or text with speech. You can also update your status on your social networking accounts.
Try "Dragon Go" different than Dragon Dictation. Go ties into Google, Wiki, Yelp, Phone Numbers, Twitter... And you can turn on location to find things near you.