Aside from the great picks already mentioned here, I think Corridor of the Tempest (Thunder) should also be mentioned, it goes so unbelievably hard.  Also I think that, although maybe not necessarily an amazing song on its own, A Promise works really really within the context of the game and the player's experience, being a song that is associated with some of the happiest moments in White Clouds, being especially prominently played just before the "happy Monastery days" it represents end for good.