Google Play offers the Relapse Records 25th Anniversary MP3 Album for free. That's a buck under the lowest price of most of these songs purchased individually elsewhere for a total savings of around $30. It features 31 tracks from Relapse Records' back catalogue, including bands like Mastodon and Dillinger Escape Plan.
Google Play offers downloads of its February Antenna 16-Track MP3 Sampler for free. (iTunes and Amazon charge 99 cents or more for most of these tracks.) It features songs from new artists such as All We Are, Air Lands, Maudlin Strangers, and Dan Mangan & Blacksmith.