I have a hacked [link|http://www.adamlotz.com/iopener.html|iopener] with a 30GB drive full of MP3s. I just boot it up and let it random play when I want to listen to some music. It's really handy for parties. It's no different than making "mix tapes" of music you already own.

99% of the music on my iopener is ripped from CDs that are stored on the other side of the room. The remainder comes from artists, such as [link|http://freezepop.net|Freezepop], who let you download tracks off their site.