This is something that’s been around since Snow Leopard, but I just discovered it yesterday (I’m slow): Highlight a block of text in Mac OSX Snow Leopard/Lion, and easily have it sent to iTunes as a spoken track.
To use this feature, first enable it in System Preferences » Keyboard » Keyboard Shortcuts » Services. In the left-hand column, select Services, then scroll down to the Text section in the right-hand window and enable ‘Add to iTunes as a Spoken Track.’
Now whenever you want to convert text to speech from something you’re reading, highlight the text, control=Click (or right-click) on it and choose ‘Add to iTunes as a Spoken Track’.
You’ll find it in iTunes as “Text to Speech”, in the Music section.
The original text to speech file is created as an AIFF file. Once it’s placed in iTunes, you’ll find it’s been converted there into the AAC VBR 128kbps format.
Note: This script throws out the AIFF version of the track once the iTunes track has converted. If you need to convert it to MP3 instead or any other format, just retrieve the file from the Finder’s trash.