The Disgaea 5 base music (the base is basically an elaborate menu really - with NPC's serving as traditional choices). I wasn't expecting a whole-ass song complete with vocals and Japanese electric jazz guitar. Also mad groovy when stoned:
Played a lot of games and yet no opening theme music has set a calmer mood than Flower. The whole OST is a step away from the chaos of life.
Had to add Uncharted 2 because Nate's Theme 2.0 was, and still is, pretty epic.