Here are a bunch of songs I generated using autotracker-bu by Ben "GreaseMonkey" Russell which is public domain python script that generates random pieces of music using the instruments built in. People over at the Ludum dare have been using it for ages to generate some music for their classic arcade games. You can get my copy of the script here
Everything it makes is also public domain so here is 18 of them that I made with it and a few code tweaks:linky to zip file
You'll need a music player like Winamp to play them and a program like schismtracker to turn them into wav files so you can convert it to other formats (or you can ask me to do it for you).