You can almost be sure that any of the free songs for the week from Amazon or iTunes (especially) is going to get big (it happened/is happening with "Love Song", "Party Rock Anthem", "Let Her Go", "Blackout", "Moneygrabber" [seriously fucking perfect live], "Little Games", "Cool Kids", "Start A Riot", and "Reflections"), so you should always get free music when it's available (if you're on a budget/prefer indie music, start using NoiseTrade; their featured band, Runaway Dorothy, is one that I'll be interviewing soon so check out their free tracks in advance of that).
Bad Suns' "Cardiac Arrest" is iTunes' free single of the week and you need to download it (from the US iTunes store). The vocals are strong and just dreamy enough to give the song a lasting quality, that circling guitar riff is about perfect for sucking you in and making you want to dance, and the rhythm is fantastically heavy. If you like what you hear, make sure to get the band's new Transpose EP, released today; it's well worth its $4 and all of the tracks are just as catchy and worthy of listening to on repeat as this track."Cardiac Arrest" Bad Suns