Android 4.1 bring a new conversational text-to-speech voice feature in US English on Nexus 7 tablet. Type text by speaking use the online speech-recognition service, so you need to put your tablet into a WiFi network.
How to use speech to Text on Nexus 7
* Touch a text field in email, Gtalk or Messaging app.
* The onscreen keyboard will pop up. Touch the Microphone key on it.
* Now speak what you want to type. To enter punctuation, just say "comma," exclamation mark," "question mark," "period," " or "exclamation point". If you pause, it will transcribe into text.