Speakables for iTunes works in conjunction with Speakable Items—the free voice recognition software included in Mac OS X—to allow you to launch playlists just by using your voice. It sells for $10.
“Speakable Items frees you from your desktop (or makes you look cool when sitting there) by allowing you to control your Mac with simple voice commands. There are many common voice commands built in that you can already use right away, or create your own. Speakable for iTunes extends the capabilities of Speakable Items by allowing you to make your Playlists ‘speakable’ (that is, they will begin playing when you say the name of the playlist)—something you can’t do with Speakable Items alone.”