Music producer Nick Pittsinger slowed Bieber’s “U Smile” down 800% and the result was ethereal magic. Find a song to experiment with and slow it down to the point where it becomes an amazing piece of ambient music. If doing this with Audacity or any other non-linear digital editor, you’ll likely have to perform multiple lengthings of the song. Be sure to pitch shift so that even though the track is longer, it doesn’t become just a low pitched version (think of the sound used in a slow-mo moment of someone yelling Nooooooo).
Here are a couple of suggested task specific tools as well:
http://hypermammut.sourceforge.net/paulstretch/
http://www.cornwarning.com/xfer/PaulStretch-2.2.2-OSX-10.6.dmg