This is a secret, don't tell anyone →
You didn't hear it from me, but do you know about Hype Machine
? It's a site what goes through all the RSS feeds looking for blog posts with MP3s in them, then aggregates them in to RSS feeds search-able by keyword.
The upshot of all this nerd talk is that you can enter an artist name, and get a list of MP3s that relate to that artist (songs, live tracks, covers) that have been posted. And what's more, you can get it as a podcast feed for your iTunes and just automagically get new stuff.
The links go stale pretty fast, and since your getting these off people's blogs, the donwload speed is all over the map, but hey, the price is right.
I can barely get my mind around this.