For all the people searching for what the song at the end of Game of Thrones tonight was, here you go:
The song is The Rains of Castomere performed by the band The National with lyrics by George R. R. Martin. According to the Westeros wiki (beware spoilers at that site), the song was written about a Tywin Lannister military victory with the following refrain:
And who are you, the proud lord said,
that I must bow so low?
Only a cat of a different coat,
that’s all the truth I know.
In a coat of gold or a coat of red,
a lion still has claws,
And mine are long and sharp, my lord,
as long and sharp as yours.
And so he spoke, and so he spoke,
that lord of Castamere,
But now the rains weep o’er his hall,
with no one there to hear.
Yes now the rains weep o’er his hall,
and not a soul to hear.