The credits theme of Dawn of the Dragon is glorious, and especially fitting thanks to the ending. It's also pretty emotional for those fans who have been around for the last ten or eleven years of the game. "There is an open door somehow it seems so familiar, we have been here before" indeed... Damn.
Gaul's theme from The Eternal Night was pretty badass, and fitting, for an ape king with dual swords and an eye laser. Here are both of his themes from the console version.
The Valley of Avalar. It's so peaceful and lovely. After an action-packed beginning trapped deep underground, and then the confusion of Twilight Falls, a wide-open level in the sunshine is just the thing to put you at ease.