I recently had a need to quickly and quietly encode some text to an audio file on my Macbook.  I found a very short, simple and effective Applescript file right on the Apple website which does just that.

The script will prompt you to choose one of the built-in system voices, then produce your file.  If you need an MP3, just open it up with iTunes and convert the track.

Sheer Brilliance!

PS: Those of you who watch Command N should try out the Zarvox voice.