I recently bought a 5th generation iPod touch, but was dismayed to learn that I can't use Siri to play music in my car because it doesn't work offline. Is there a voice control app that I can use to choose songs without a wifi connection?
If you're willing to sacrifice Siri for the ability to control your music with your voice, you could turn off Siri in Settings>General>Siri, which'll make your iPod respond to a held-down Home button with the classic Voice Control interface instead. A Google search is telling me that that one works offline!
For more information about non-Siri Voice Control, check out Apple's support page. Here's what it says about music playback:
You can play all songs in an album, playlist, or by an artist. The device won't recognize commands to play a particular song.
If you can't get the device to recognize the album or artist name, try telling it to play a playlist.
If an artist has "The" in the name, say it.