Audacity is one of the best free Sound/Audio editing programs i have ever seen. It's easy, fun, and awesome. If you want to see an example song/tutorial, here's my tutorial on it (possibly the first) = http://scratch.mit.edu/projects/Simtropolis/1299174 . It will also have the download link in it, so if you want to try it, you don't need to search it down.
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Audacity is great! Here's your link made clickable using the tags that sanddude discusses
http://scratch.mit.edu/projects/Simtropolis/1299174
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