It's not quite as robust as Siri on iOS, but Android’s built-in voice recognition software is surprisingly capable. Try it out: from a text input field, click the microphone button to the left of the space bar. You'll be able to dictate text messages, fill a field, or even search the Web without having to tap anything out with your thumbs. (To get that last function, Froyo and Gingerbread users might have to download Google's free Voice Search app.)
Of course, the text recognition engine sometimes delivers less-than-accurate, or downright comedic, results. If that's happening more often than you'd like, try turning on personalized voice recognition in your device’s Settings. Tap "Language and Input," then look for the "Text-to-speech output" option under the Speech section. Turning on Personalized Recognition on the following page will help give you more accurate speech synthesis over time. This tip requires a little patience – you might not notice much improvement in transcription accuracy at first, but over time your device will adjust to your personal inflections.