I mostly listen to classic rock and electronic dance music.
Being middle aged, I pretty much accumulated every classic rock song/album on cd that I liked before mp3s even existed. Barring cd rot, I'm probably all set there. Though once in a while I will get something from Amazon that I missed. (I actually did get one song back in the DRM music days, a WMA file from Walmart. Journey of the Sorcerer by the Eagles (song used in The Hitchhiker's Guide to the Galaxy).
It's nice though that cd is where it's stopped. Instead of record, 8-track, casette tape, cd, new thing (like VHS, DVD, Blu Ray).
And for electronic dance music, many DJs make their radio shows available for free to download, either on their own site or itunes. So I just get that. Just a few shows is really more new music than I can listen to in a week.
For example:
http://suzysolar.com/suzysolar/category/tracklists/