I saw AimeStreet in a recent article. It makes it easy for new artists to distribute digital music. From the buyer's side, a track ranges from free to 98 cents. The price rises as it becomes more popular. They can buy individual tracks or whole albums at once.
From the artist's side, they make 70% of each sale (after it sells $5). I'm not sure but that seems like a decent payout rate considering that there are no up-front fees and it isn't an exclusive agreement so you can sell through other channels. You only get paid quarterly though.
There doesn't seem to be an affiliate program for the site but you'd think they'd consider one. You can embed a player in other sites to promote artists you like for free. I picked some random Christian artist to embed below. It's better than the current best-selling artist on the site.