Or you could try the SimpleSDAudio library, which uses PWM to output sound direct form the Arduino. It reads from an SD card.
The only Caveat is that you have to convert the files first, but that is a simple drag and drop operation.
The sound quality is very respectable and you can do 8 bit Mono and Stereo and even a pseudo 16 bit Mono and Stereo.
http://www.hackerspace-ffm.de/wiki/index.php?title=SimpleSDAudio