If you’re an Amazon associate (if not, go ahead an become one), you can earn 20% commission on MP3 downloads from Amazon. There are currently over 2 million songs from 180.000 artists sold in DRM-free format on Amazon’s new MP3 downloads store.
This offering is valid through December 31st, when the commissions will go down to only 10%, so make that money while you can! More details on Amazon’s associate blog.