Google Play offers the Various Artists Blues Pioneers MP3 Album for free. That's $10 less than buying these tracks separately. It includes 10 songs from such artists as Blind Boy Fuller and Mamie Smith.
Google Play offers downloads of its August Antenna 13-Track Sampler MP3 Album for free. (iTunes and Amazon charge 99 cents or more for most of these tracks.) It includes songs from such artists as Rozwell Kid, Ducktails, Jenny Amy Helm, and Kaleo.