From WPCentral.com:
Hey DJ! for Windows Phone is a hands-free music player that allows you to play music in your collection using your voice. All you need to do is say the name of the song, artist, album, genre or the playlist you want to play.
The version 2.3 of the app just went live in the Store and as part of a New Year promotion, the full version is free until January 14.
The latest version includes new voice commands - next track, previous track, pause music, resume music, shuffle on/off, repeat on/off. The voice commands are available in English as of now, although other languages are coming soon. There are some bug fixes and stability improvements as well.
This is a great app to control your music without touching your phone. The recognition works really well in my experience. Certainly worth checking out as it's useful when driving and using a Bluetooth kit.