unlimited drm free mp3s for free?
To be honest I think that is legally impossible as it's too easy to abuse.
If you're willing to compromize there are a few options:
7digital: Legal, drm free, but pay per song/album
Slacker: Legal, free (ads), but locked down tighter than a nun's knickers
<redacted>: free, drm free, but so illegal I can't name it.