You could try mood based ads. Very difficult to sell to an advertiser, but it could have some interesting applications. I wonder if depressed or happy people buy more.

there could also be potential for B2B services: think airport lounges, auto salons, etc etc ...

Buy buttons on every track. Lots of music I've never heard about that I might like to download to my music player.

EDIT: There are buy buttons on every track, but frankly they're almost too inobtrusive - I didn't notice them at first.